Early Mesozoic paleogeography and tectonic evolution of

ABSTRACT

This study assesses early Mesozoic prove-nance linkages and paleogeographic-tectonic models for the western United States based on new petrographic and detrital zircon data from Triassic and Jurassic sandstones of the “Izee” and Olds Ferry terranes of the Blue Mountains Province, northeastern Oregon. Triassic sediments were likely derived from the Baker terrane offshore accretionary sub-duction complex and are dominated by Late Archean (ca. 2.7–2.5 Ga), Late Paleo protero-zoic (ca. 2.2–1.6 Ga), and Paleozoic (ca. 380–255 Ma) detrital zircon grains. These detrital ages suggest that portions of the Baker ter-rane have a genetic affinity with other Cor-dilleran accretionary subduction complexes of the western United States, including those in the Northern Sierra and Eastern Klamath terranes. The abundance of Precambrian grains in detritus derived from an offshore complex highlights the importance of sedi-ment reworking. Jurassic sediments are dominated by Mesozoic detrital ages (ca. 230–160 Ma), contain significant amounts of Paleozoic (ca. 290, 380–350, 480–415 Ma), Neoproterozoic (ca. 675–575 Ma), and Meso-protero zoic grains (ca. 1.4–1.0 Ga), and have lesser quantities of Late Paleoprotero-zoic grains (ca. 2.1–1.7 Ga). Detrital zircon ages in Jurassic sediments closely resemble well-documented age distributions in trans-continental sands of Ouachita-Appalachian provenance that were transported across

the southwestern United States and modi-fied by input from cratonal, miogeoclinal, and Cordilleran-arc sources during Triassic and Jurassic time. Jurassic sediments likely were derived from the Cordilleran arc and an orogenic highland in Nevada that yielded recycled sand from uplifted Triassic backarc basin deposits. Our data suggest that numer-ous Jurassic Cordilleran basins formed close to the Cordilleran margin and support a model for moderate post-Jurassic translation (~400 km) of the Blue Mountains Province.

INTRODUCTION

There is significant controversy regarding the early Mesozoic paleogeography and tectonic evolution of allochthonous and parautochtho-nous terranes of the western U.S. Cordillera. Workers generally agree that Cordilleran ter-ranes represent oceanic and craton-fringing crustal fragments that were accreted to western Laurentia prior to development of an integrated Andean-type convergent margin in Cretaceous time; however, the configuration and construc-tion of the “pre-Andean” western Laurentian margin remain debated. Numerous contrast-ing tectonic models have been proposed to explain early Mesozoic development of the continental-margin arc in Arizona-California and marginal arc-basin complexes of the Sierra Nevada foothills and Klamath Mountains (Fig. 1; e.g., Harper and Wright, 1984; Ingersoll and Schweickert , 1986; Burchfiel et al., 1992; Saleeby, 1992; Saleeby and Busby-Spera, 1992; Dickinson, 2000, 2008; Dickinson et al., 1996; Day and Bickford, 2004; Gray and Oldow, 2005; Snoke, 2005; Ernst et al., 2008), and the Blue Mountains Province (Dickinson, 1979, 2000; Burchfiel et al., 1992; Saleeby, 1992; Saleeby and Busby-Spera, 1992; Avé Lallemant, 1995;

Vallier, 1995; Dorsey and LaMaskin, 2007, 2008). This proliferation of models reflects, in part, insufficient constraints on provenance links to North America, the early Mesozoic latitude of marginal arc-basin complexes, and the amount of subsequent post-Jurassic margin-parallel displacement.

Accreted terranes of the Blue Mountains Province in northeastern Oregon and western Idaho preserve one of the most complete and least-deformed early Mesozoic stratigraphic records in the western U.S. Cordillera (Fig. 1; see stratigraphic compilations in Saleeby and Busby-Spera, 1992). Marine deposition took place in this region from Late Triassic through early Late Jurassic time, preserving a record of terrane and marginal-basin evolution (Dickinson and Vigrass, 1965; Dickinson and Thayer, 1978; Dickinson, 1979; Vallier, 1995; Dorsey and LaMaskin, 2007, 2008; LaMaskin et al., 2008a). In this paper, we use petrographic and detrital zircon U-Pb age data from Trias-sic and Jurassic Cordilleran margin sedimen-tary basins of the Blue Mountains Province in Oregon to assess potential linkages to cratonal North America and place new constraints on tectonic and paleogeographic models for the western United States (Fig. 2). Our objectives are to (1) test and refine existing correlations of early Mesozoic sedimentary successions from eastern Oregon to western Idaho, (2) document the evolution of sediment source areas through time, (3) evaluate paleogeographic and paleo-tectonic models for the Blue Mountains, and (4) assess the implications of our results for the pre-Cretaceous configuration of the western Laurentian margin.

In the John Day region of northeastern Ore-gon, sediment is interpreted to have been derived from both outboard subduction-accre tionary complexes and inboard volcanic-dominated

For permission to copy, contact [email protected] © 2011 Geological Society of America

1939

GSA Bulletin; September/October 2011; v. 123; no. 9/10; p. 1939–1965; doi: 10.1130/B30260.1; 15 figures; 3 tables; Data Repository item 2011188.

†Current address: Department of Environmental Sciences, Wisconsin Geological and Natural History Survey, University of Wisconsin–Extension, 3817 Mineral Point Road, Madison, Wisconsin 53705-5100, USA; [email protected]

Early Mesozoic paleogeography and tectonic evolution of the western United States: Insights from detrital zircon U-Pb

geochronology, Blue Mountains Province, northeastern Oregon

Todd A. LaMaskin1,†, Jeffrey D. Vervoort2, Rebecca J. Dorsey1, and James E. Wright3

1Department of Geological Sciences, University of Oregon, 1272 University of Oregon, Eugene, Oregon 97403-1272, USA2School of Earth and Environmental Sciences, Washington State University, Pullman, Washington 99164-2812, USA3Department of Geology, University of Georgia, 308 Geography-Geology Building, 210 Field Street, Athens, Georgia 30602-2501, USA

on August 26, 2011gsabulletin.gsapubs.orgDownloaded from

http://gsabulletin.gsapubs.org/

LaMaskin et al.

1940 Geological Society of America Bulletin, September/October 2011

sources (Dickinson and Thayer, 1978; Dick-inson, 1979; Dickinson et al., 1979). This sandstone provenance framework provides im-portant constraints for understanding detrital zircon age distributions in the same deposits. Our new detrital zircon data are consistent with—and provide new insights into—previ-ously documented shifts in sandstone compo-sition from Late Triassic to early Late Jurassic time (e.g., Dickinson, 1979; Dickinson et al., 1979). In particular, these data suggest that Jurassic basins of the Blue Mountains Province were linked to a large, Triassic–Jurassic trans-continental sediment-dispersal system (i.e., Rahl et al., 2003; Dickinson and Gehrels, 2003; 2009), either directly or via tectonic and sedi-mentary recycling.

The presence of Laurentian detrital zircon grains in sediments of the Blue Mountains Province has implications for the proximity of

Late Proterozoic to Permian miogeoclinal rocks

North American craton

Pre-Cretaceous subduction complexes

Cenozoic, undivided

Cretaceous plutonic belts

Wrangellia terrane and metamorphic rocks of the Washington Cascades

Paleozoic and Mesozoic eugeoclinal rocks

North American fringing-arc terranes

Outboard arc and ophiolitic terranes

BM

Cordilleran continental arcMSNI FaultKM

SN

EXPLANATION

118°W

36°N

40°N

44°N

48°N

MT

WY

UTAZ

122°W

ColoradoPlateau

32°N

114°W

114°W122°W 118°W 110°W

110°W

WAOR

0 200kmN

NV

BRT

IDORCA

CONM

LFT

B

CANADA

36°N

40°N

44°N

48°N

32°N

Cordilleranthrustbelt

Figure 2

Modified from Wyld et al. (2006)

Figure 1. Simplified pre-Tertiary geology of the western United States, modified from Wyld et al. (2006). BM—Blue Mountains Province; BRT—Black Rock terrane; KM—Klamath Mountains; SN—Sierra Nevada; MSNI—Mojave–Snow Lake–Nevada–Idaho fault (after Wyld and Wright, 2005); LFTB—Luning-Fencemaker thrust belt.

Figure 2 (on following page). Geologic map of the Blue Mountains Province, modified from LaMaskin (2009). Ages of plutons are shown where data are available; z—U-Pb zircon age; K-Ar—potassium-argon age. Question marks indicate uncertain terrane affiliations and/or terrane boundary locations. The Bourne and Greenhorn subterranes, Grindstone terrane, and Burnt River Schist are here considered subterrane-level units of the Baker terrane. Pz—Paleozoic; Mz—Mesozoic; Tr—Triassic; Jr—Jurassic; K—Cretaceous; MS—megasequence (after Dorsey and LaMaskin, 2007); BRS—Burnt River Schist; BMB—Bald Mountain batholith; WB—Wallowa batholith; PCF—Poison Creek fault; Cpx.—complex; Ldg.—landing; WA—Washington; OR—Oregon; ID—Idaho. Data were compiled from nu-merous sources, including Dickinson and Vigrass (1965); Brown and Thayer (1966, 1977); Thayer and Brown (1966); Hendricksen et al. (1972); Brooks et al. (1976); Dickinson and Thayer (1978); Brooks (1979); Walker and MacLeod (1991); Walker (1986, 1995); Vallier (1995, 1998); Ashley (1995); Ferns and Brooks (1995); Leeman et al. (1995); Ferns et al. (2001); Lewis (2002); Lund (2004); Kays et al. (2006); Dorsey and LaMaskin (2007); Mann and Vallier (2007); Parker et al. (2008); Unruh et al. (2008); J. Schwartz (personal commun., 2009), and K. Johnson (personal commun., 2009).



Early Mesozoic paleogeography and tectonic evolution of the western United States

Geological Society of America Bulletin, September/October 2011 1941

Iron

side

Mtn

.

Cu

dd

yM

tns.

WA

LL

OW

AT

ER

RA

NE

OR

WA

?

OR

ID

OR

ID

WA

JOH

N D

AY

R

EG

ION

Mtn

. Hom

e

met

amor

phic

com

plex

ID

253

z 2

15z

200

k-ar

212

-21

8z

?B

RS

235

z

zone

PC

F

BM

B

WB

?

141

z

Bak

er

Spa

rta

Cpx

.

Bo

urn

e

BR

S

Can

yon

Mtn

. Cpx

.

147

z

Dix

ieB

utte

Western Idahoshear

John

Day

Gre

enh

orn

Coo

n H

ollo

w

Pitt

s.Ld

g.

??

Idah

oB

atho

lith

263z26

2-24

2z

263z

225-

228z

230

z

278

-268

z

137k

-ar

124

z

Bo

urn

e

Mitc

hell I

nlie

r

Pz-

Mz

Vol

cani

c an

d S

edim

enta

ry

Wal

low

a Te

rran

e

Pz-

Mz

serp

entin

ite a

ndch

ert-

argi

llite

mel

ange

, sc

hist

Bak

er T

erra

ne

Old

s F

erry

Ter

ran

e

Rig

gins

Gro

up a

ndO

rofin

o S

erie

s m

etam

orph

ic

Sal

mo

n R

iver

Bel

t

Tr-

Jr V

olca

nic

and

Sed

imen

tary

Tr-

JrS

edim

enta

ry a

nd

Vol

cani

c ro

cks

ofM

S-1

, Joh

n D

ay r

egio

n

Sch

ist,

Gne

iss,

and

A

mph

ibol

ite o

f unk

now

nor

igin

Cre

tace

ous

Sed

imen

tary

Pz

Maf

ic-U

ltram

afic

Pz

Inte

rmed

iate

-Maf

ic

Tria

ssic

Fel

sic-

Inte

rmed

iate

Mid

dle

Jura

ssic

-Ear

ly

Cre

tace

ous

Inte

rmed

.

Cre

tace

ous-

Pal

eoge

ne

EX

PL

AN

AT

ION

Sta

te B

orde

rTe

rran

e B

dy.

Cov

ered

Terr

ane

Bdy

.E

xpos

ed

Sub

-ter

rane

Bdy

..(a

ppro

x.)

Jr S

edim

enta

ry a

ndV

olca

nic

rock

s of

MS

-2

050

kmN

Hun

tingt

on

?

Juni

per

Mtn

.

223k

-ar

blu

esch

ists

Grindst

one

157

z 147

z

162

z 1

46z

146

z

226

z

231

z

146

z 1

54z

244

z

146

z

158z

140z 16

1z

BA

KE

RT

ER

RA

NE

OL

DS

FE

RR

YT

ER

RA

NE

“IZ

EE

TE

RR

AN

E”

B

(isl

and

arc

as

sem

bla

ge)

(isl

and

arc

as

sem

bla

ge)

(su

bd

uct

ion

-acc

reti

on

ary

com

ple

x)

(cla

stic

su

cess

ion

)

148

z

A

Jr-K

Sed

imen

tary

roc

ks o

fth

e C

oon

Hol

low

For

mat

ion

Plu

ton

ic R

ock

s

148

z

Fig

ure

2.



LaMaskin et al.


so-called “allochthonous” Cordilleran basins to the North American craton. In addition, our results highlight the complexities of matching detrital zircon data to potential source regions and illustrate the importance of sedimentologic and stratigraphic setting for making reliable interpretations.

GEOLOGIC SETTING

Regional Geology

The Blue Mountains Province in Oregon, Idaho, and Washington (Fig. 2) is an assem-blage of variably metamorphosed accreted ter-ranes that are situated in a key position between coeval accreted terranes of California, Nevada and southern British Columbia (Hamilton, 1963; Armstrong et al., 1977; Vallier, 1977, 1995; Dickinson and Thayer, 1978; Brooks and Vallier, 1978). It has been divided into two late Paleozoic to early Mesozoic volcanic island-arc assemblages (the Wallowa and Olds Ferry terranes), a Paleozoic to early Mesozoic sub-duction-accretionary complex (Baker terrane), and a Triassic–Jurassic clastic sedimentary suc-cession (Izee terrane; Silberling et al., 1984). Rocks of all four terranes appear to have been affected by Late Jurassic deformation (Avé Lalle mant, 1995), and terrane-bounding faults are crosscut by Late Jurassic to Early Creta-ceous granodioritic plutons that indicate ter-rane amalgamation prior to ca. 144 Ma (Fig. 2; Walker, 1986, 1989). Faunal data suggest that during Late Triassic time, rocks of the Blue Mountains Province, which originated in an eastern Pacific, Central Tethyan location, were transported northward to Northern Tethyan lati-tudes by Early Jurassic time, and to boreal lati-tudes by Middle Jurassic time (Pessagno and Blome, 1986; Pessagno, 2006). Although we retain the conventional terminology for terranes in the Blue Mountains Province, some of these tectonostratigraphic units do not have entirely distinct origins and are, to varying degrees, genetically related (cf. Dorsey and LaMaskin, 2007, 2008; Dickinson, 2008; LaMaskin et al., 2008a; Schwartz et al., 2010).

The upper Paleozoic to lower Mesozoic Wallowa terrane is an intra-oceanic volcanic arc succession that occupies the most out-board position in the Blue Mountains Province (Fig. 2; Vallier, 1977, 1995; Walker, 1986, 1995; LaMaskin et al., 2008a). It has been correlated to either the Wrangellia terrane (Wernicke and Klepacki, 1988; Dickinson, 2004) or the Stikine terrane in British Columbia (Mortimer, 1986; Oldow et al., 1989; Yancey and Stanley, 1999). The Upper Triassic to Lower Jurassic Olds Ferry terrane is a volcanic arc succession that

occupies the most inboard position in the Blue Mountains Province (Brooks and Vallier, 1978; Brooks, 1979; Vallier, 1995; Walker, 1995; Tumpane et al., 2008; Tumpane and Schmitz, 2009; LaMaskin, 2008). The Olds Ferry ter-rane has been correlated with the Quesnel terrane in British Columbia (Dickinson, 2004) and the Black Rock terrane in Nevada (Wyld and Wright, 2001; Dorsey and LaMaskin, 2007) and likely represents a Japan-type, continent-fringing volcanic arc (LaMaskin et al., 2008a). Permian plutonic rocks (ca. 286–268 Ma) of the Canyon Mountain complex and Aldrich Moun-tains of central Oregon may represent exhumed forearc crust of the Olds Ferry arc (e.g., Avé Lallemant, 1995), or these rocks may be more appropriately grouped with the Baker terrane.

The Baker terrane accretionary subduction complex (Fig. 2) is situated between the Wallowa and Olds Ferry terranes and includes both island-arc and oceanic-related sedimentary, vol-canic, and plutonic rocks (Carpenter and Walker, 1992; Hotz et al., 1977; Bishop, 1995a, 1995b; Ferns and Brooks, 1995; Leeman et al., 1995; Vallier, 1995). Sedimentary units in the Baker terrane include variably deformed Devonian through Triassic clastic and carbonate succes-sions with minor occurrences of Jurassic strata (Jones et al., 1976; Coward, 1983; Morris and Wardlaw, 1986; Blome and Nestell, 1991; and references therein). Regionally, portions of the Baker terrane have been interpreted to represent a disrupted forearc region (Greenhorn subter-rane) and an associated oceanward accretionary prism (Bourne subterrane; Ferns and Brooks, 1995; Schwartz et al., 2010). The Baker terrane is widely considered to be correlative to simi-lar rocks of the Cache Creek terrane in British Columbia and the Eastern Hayfork and Stuart Fork terranes and Central metamorphic belt in the Klamath Mountains (Saleeby, 1983; Miller, 1987; Oldow et al., 1989; Hacker and Goodge, 1990; Burchfiel et al., 1992; Wyld et al., 2006; Kays et al., 2006).

The Izee terrane, as traditionally defined (Fig. 2), consists of (1) Triassic and Jurassic sedi-mentary rocks in central Oregon that rest depo-sitionally on the Baker terrane, and (2) Jurassic deposits in eastern Oregon and western Idaho, which are thrust to the southeast over the Tri-assic and Jurassic Olds Ferry terrane (Brooks, 1979; Dickinson, 1979; Silberling et al., 1984; Tumpane, 2010). Correlation of Middle Juras-sic rocks in the John Day region of Oregon with the Coon Hollow Formation in the Wallowa terrane (Pessagno and Blome, 1986; White et al., 1992) has led workers to interpret a strati-graphic overlap assemblage that linked the Blue Mountain terranes by Early to Middle Jurassic time (i.e., Pessagno and Blome, 1986; White

et al., 1992; Dorsey and LaMaskin, 2007, 2008; LaMaskin et al., 2008a).

Rocks of the Blue Mountains Province are overthrust in the northeast by high-grade meta-morphic rocks of the Salmon River belt (Lund and Snee, 1988; Selverstone et al., 1992; Man-duca et al., 1992, 1993; Lund, 2004; Gray and Oldow, 2005; Lund et al., 2008). The Salmon River belt is bounded on the east by the Western Idaho shear zone (Fig. 1), a complex structural boundary with the Laurentian continental mar-gin. The Western Idaho shear zone is overprinted by Late Cretaceous to Early Tertiary plutons that define an anomalously sharp discontinuity between accreted oceanic and continental litho-sphere (Lund and Snee, 1988; Getty et al., 1993; Manduca et al., 1992, 1993; McClelland et al., 2000; Tikoff et al., 2001; Selverstone et al., 1992; Giorgis et al., 2005, 2008).

It has been postulated that during Early(?) to Late Cretaceous time, northward translation of the Blue Mountains Province was accommo-dated by various amounts of dextral-transpres-sive shear along the Western Idaho shear zone. Restoration of <100 km of displacement (e.g., Saleeby and Busby-Spera, 1992; McClelland et al., 1992; Dickinson, 2004, 2006; Gray and Oldow, 2005) suggests that during pre-Creta-ceous time, the Blue Mountains Province was located outboard of a cryptic continental mar-gin, the history of which has been obscured by pluton emplacement and Cretaceous short-ening in the Salmon River belt and Western Idaho shear zone. Alternatively, restoration of ~400 km of dextral displacement (e.g., Wyld and Wright, 2001; Wright and Wyld, 2007) juxtaposes the Blue Mountains Province with the Triassic Cordilleran fringing arc in west-ern Nevada (Black Rock terrane), which was separated from the continent by an extensional backarc basin (Speed, 1978; Oldow, 1984; Oldow et al., 1989; Smith et al., 1993; Wyld, 2000, 2002). Closure of the backarc basin in Jurassic time resulted in accretion of the fringing arc, crustal shortening and thicken-ing, and development of a Jurassic orogenic belt in western and central Nevada (Luning-Fencemaker fold-and-thrust belt; Speed, 1978; Oldow et al., 1989; Wyld, 2002; Wyld et al., 2003). According to a third hypothesis, res-toration of >1000 km of displacement (e.g., Housen and Dorsey, 2005, post–94 Ma) places the Blue Mountains Province at the approxi-mate latitude of southwestern Arizona and northern Mexico as an offshore arc of uncertain relationship to the Triassic–Jurassic continen-tal magmatic arc (Saleeby and Busby-Spera, 1992; Dickinson and Lawton, 2001). Detrital zircon data presented here serve as a partial test of these different proposed reconstructions.





Early Mesozoic Stratigraphy and Structure of Northeastern Oregon and Western Idaho

Megasequence StratigraphyWe divide the early Mesozoic sedimen-

tary succession of northeastern Oregon and western Idaho into two regionally correlative, unconformity-bound megasequences, mega-sequence 1 and megasequence 2 (Figs. 3 and 4; Dorsey and LaMaskin, 2007, 2008; LaMaskin

et al., 2008a, 2009). A megasequence is a large-scale, composite stratal unit (hundreds to thou-sands of meters thick and tens of millions of years in duration) that accumulates during a distinct phase of basin evolution. Boundaries between megasequences typically form due to changes in tectonic boundary conditions that control basin development (e.g., Phinney et al., 1999). They differ from traditional stratigraphic “sequences ” (cf. Vail et al., 1977; Van Wagoner

et al., 1990) by being thicker, longer-duration, composite units bounded by angular uncon-formities that record major changes in regional tectonic setting.

John Day RegionEarly Mesozoic sedimentary rocks are tra-

ditionally assigned to the “Izee terrane” in the John Day region of northeastern Oregon. Here, early Mesozoic rocks are found in depositional

W E

NW SE

Forbes Butte Magpie TableIzeeSuplee

CCF

PCFmelange

JsJt

Jl

Jk 1500 m

500 m

1000 m

1000 m

3000 m

Jmc500 m

3250 m

TRfc 4500 m

TRl

Baker Terrane (Pz-Mz):Subduction-Accretionary Complex

Fields Creek Fm: synthrusting

Silvies Valley

TRfc

Jl Lonesome FmJt Trowbridge FmJs Snowshoe FmJm Mowich GpJk Keller Creek ShaleJmc Murders Creek GwkeTRl Laycock GraywackeTRfc Fields Creek FmTRrc Rail Cabin ArgilliteTRvbr Brisbois Mbr TRvb Begg Mbr

Pz subduction melange

Cenozoic rocks

Topographic profile V.E. = 1.5xremoved in Izee area for clarity

15002000

80706050403020100Distance (km)

Distance (km)

1000500

0

Ele

vatio

n (m

)

TRrc

MS

-1M

S-2

Jm

AldrichMts.

Group

Vester Fm

3750 m

0 5 10 15

Snake RIverWillow SpringI-84WeatherbyConnor Ck.

fault

Huntington Fm.Olds Ferry arc

Baker Terrane (Pz-Mz):

Weatherby Formation

Weatherby Fm.Jet Creek Mbr.

?

A

B

TRhJwj

Jw

TRvb

TRvbrTRvb

TRvbr?

?

06139

06004

0611806137

07015

0613506152

06210

07033

04064

Upper FlyschLower Flysch Jet Creek Mbr

WeatherbyFm.

TRh Huntington Fm. - Olds Ferry Arc

Jwj

Jw

MS-1

MS-2

Figure 3. Schematic cross sections of Mesozoic rocks in the John Day and Huntington, Oregon, areas prior to Late Jurassic deformation. Lines of section are shown on Figure 2. Black zircon crystals and sample numbers indicate approximate detrital zircon sample locations. Formation names in bold italics (lower left insets) indicate sampled intervals. MS—megasequence. (A) Stratigraphic-structural reconstruc-tion of John Day region modified from Dorsey and LaMaskin (2007). Image is projected into E-W line of section using maps and data from Dickinson and Thayer (1978), Dickinson and Vigrass (1965), and Brown and Thayer (1966). CCF—Camp Creek fault; PCF—Poison Creek fault. (B) NW-SE cross section of Huntington, Oregon, area modified from Avé Lallemant (1983).



LaMaskin et al.


and fault contact with disrupted Paleozoic to Mesozoic basement of the Baker terrane, in-cluding intrusive rocks of the Canyon Moun-tain Complex (Figs. 3A and 4; Dickinson and Vigrass , 1965; Brown and Thayer, 1977; Dick-inson and Thayer, 1978; Dickinson, 1979).

Megasequence 1. Rocks of megasequence 1 include: (1) the Vester Formation (~3750 m), which consists of chert-rich conglomerate and turbiditic sandstone with lesser amounts of black shale, polymict breccia, and local volcanic rocks (Dickinson and Vigrass, 1965; Brown and Thayer, 1977; Dickinson and Thayer, 1978); (2) the Fields Creek Formation (~4500 m), which is the lower portion of the Aldrich Moun-tains Group and represents a turbiditic succes-sion of fine sandstone and black shale with large chaotic slide breccias and olistostromes at the base (Brown and Thayer, 1977; Dickinson and Thayer, 1978); and (3) the Keller Creek Shale (~1500 m), which includes black shale and vol-

caniclastic “graywacke” sandstone (Brown and Thayer, 1977).

The Middle (?) to Late Triassic Vester and Fields Creek Formations of megasequence 1 were derived from the Baker terrane (an out-board source) as indicated by the presence of (1) voluminous reworked chert clasts with radio-laria that match Baker terrane faunas, (2) olisto-stromes that match the lithologies of plutons and sedimentary units in the Baker terrane located to the northwest, and (3) abundant southeast-directed paleocurrent data (modern coordinates; Dickinson and Thayer, 1978; Dickinson, 1979; Blome et al., 1986; Yeh, 1989; Blome and Nest-ell, 1991; Carpenter and Walker, 1992). Late Triassic uplift and erosion of the Baker terrane that caused chert-rich detritus to be shed east-ward into a large syntectonic basin in the John Day region may have been caused by local-ized back thrusting (Dickinson, 1979), nascent arc-arc collision between the Wallowa and

Olds Ferry arcs (Dorsey and LaMaskin, 2007, 2008), or from collisional events involving other crustal blocks within the Baker terrane that cur-rently are not well understood.

Rocks of megasequence 1 record marine deposition in actively deforming, convergent fault-bounded basins (Brown and Thayer, 1977; Dickinson and Thayer, 1978; Dickinson, 1979). Late Triassic to Early Jurassic synde-positional deformation (D

1 of Avé Lallemant,

1995) is recorded by north-northeast–trending faults and folds (modern coordinates) associ-ated with cannibalization of older deposits. Deformed Late Triassic to Early Jurassic megasequence 1 rocks in the John Day region are overlain by less-deformed Lower Jurassic shallow-marine deposits of megasequence 2 (Dickinson and Vigrass, 1965; Brown and Thayer, 1977; Dickinson and Thayer, 1978; Dickinson, 1979; Avé Lallemant, 1995; Dorsey and LaMaskin, 2007).

ANIS.

LADIN.

CARN.

NOR.

RHAET.HETT.SINEM.

PLIEN.

TOAR.

AALEN.

245.0±1.5

237.0±2.0

228.0±2.0

216.5±2.0

203.6±1.5199.6±0.6196.5±1.0

189.6±1.5

183.0±1.5

175.6±2.0171.3±3.0

M

L

E

Jura

ssic

Tria

ssic

BAJ.

BATHO.

CALLO.

OXFOR.

M

L

167.7±3.5

164.7±4.0

161.2±4.0

155.7±4.0

Age (Ma)

270.6±0.7

299.0±0.8

Late

EarlyPer

mia

n

Vester Fm.

ME

GA

-S

EQ

UE

NC

E 1

ME

GA

-S

EQ

UE

NC

E 2

ME

GA

-S

EQ

UE

NC

E 1

ME

GA

-S

EQ

UE

NC

E 2

251.0±0.4Early

Deep Marine Shale

Marine Shale and sandstoneturbidites

Fluvial to Shallow MarineSandstone and Conglom.

Marine Limestone

Submarine-Fan Sandstone and Conglomerate

Predominantly Volcanic with Sandstone and Congl.

Marine Sandstone

Hiatus

Detrital-Zircon Sample Location

Marine Calcareous Sandstone

Marine Calcareous Siltstone and Shale

Marine Sandstone Siltstone and Shale

Cherty Argillite, Sandstone,Serpentinite melange

Extrabasinal Olistoliths

EXPLANATION

John Day Region Eastern Oregon-Western Idaho

?

?

?

JettCreekMbr.

AldrichMtns.Gp.

Graylock & Rail

Cabin fms.

Baker Terrane /Greenhorn Subterrane /Canyon Mtn. Complex

Bris. mbr.

Suplee Izee

Basement not exposed

Begg mbr.

04064

07033

06210

07016

06135

06152

06137

06118

06004

06139

Lonesome Fm.

Snowshoe Fm.

Mowich Group.

Trowbridge Fm.

Keller Ck. Sh.

Fields Ck. Fm.

WeatherbyFm.

HuntingtonFm.

Figure 4. Sample locations (zircon crystal shapes) plotted on a chronostratigraphic correlation chart for sedimentary and volcanic rocks in the Blue Mountains. Bris.—Brisbois; mbr.—Member; Ck.—creek; Gp.—group. Figure is modified from Dorsey and LaMaskin (2007). See Dorsey and LaMaskin (2007) for additional data sources.





Megasequence 2. Deposits of megasequence 2 overlie Triassic to Early Jurassic rocks and struc-tures along an angular unconformity, and they are not affected by the first major deformation episode in the area (D

1 of Avé Lallemant, 1995).

Megasequence 2 begins with ~2500 m of Lower and Middle Jurassic volcaniclastic sedimentary and minor volcanic rocks of the Mowich Group and Snowshoe Formation (Figs. 3A and 4). These deposits record Jurassic transgression from ca. 190 to 161 Ma, concluding with depo-sition of black shales of the Trowbridge For-mation. The overlying Lonesome Formation records subsequent deposition of an ~3000-m-thick regressive sequence of sandy volcanicla-stic turbidites that display a notable increase in metamorphic and sedimentary lithic fragments during Callovian time (Dickinson, 1979; Dick-inson et al., 1979).

Deposits of megasequence 2 were previously interpreted to be derived from inboard sources, based in part on abundant west-northwest–directed paleocurrent indicators (Dickinson and Thayer, 1978; Dickinson, 1979; Dickinson et al., 1979). Strongly enriched trace-element geochemistry and unradiogenic Nd isotopic compositions (negative eNd values) of mega-sequence 2 mudrocks support the idea that Middle to early Late Jurassic sediments in the John Day region received input from inboard continental sources (LaMaskin et al., 2008a, 2008b). Megasequence 2 deposits are variably deformed by Late Jurassic contractile folds and faults (D

2 of Avé Lallemant, 1995).

Eastern Oregon–Western IdahoMegasequence 1. In eastern Oregon and

western Idaho, Triassic through Lower Jurassic volcanic and volcaniclastic rocks of the Olds Ferry terrane comprise megasequence 1 (lo-cally the Huntington Formation; Avé Lallemant, 1983, 1995; Brooks et al., 1976; Brooks, 1979; Payne and Northrup, 2003; San Filippo, 2006; Dorsey and LaMaskin, 2007; LaMaskin, 2008; Tumpane et al., 2008; Tumpane and Schmitz, 2009). These rocks are overlain along a poorly understood unconformity and SE-vergent shear zone by megasequence 2 sedimentary rocks of the Lower to Middle Jurassic Weatherby Forma-tion (Figs. 3B and 4).

Megasequence 2. The Weatherby Forma-tion includes a basal unit of red and green volcaniclastic conglomerate (~10–250 m; the Jet Creek–McChord Butte member), overlain by ~5000–7000 m of Lower to Middle Juras-sic quartzose and volcaniclastic sandstone and mudstone (Jurassic Flysch of Brooks and Vallier , 1978; Brooks, 1979; Imlay, 1986; Hooper et al., 1995; Payne and Northrup, 2003). It is widely agreed that the Weatherby Formation in eastern

Oregon and western Idaho correlates with the megasequence 2 Jurassic succession in the John Day region. Previous workers concur that rocks of both successions represent forearc or intra-arc deposits related to east-dipping subduction of an oceanic plate beneath the Olds Ferry arc (e.g., Dickinson, 1979; Vallier, 1995; Avé Lalle-mant, 1995; Gray and Oldow, 2005). Recent studies have proposed a new model—based on regional stratigraphic relationships and the paleogeographic reconstruction of Wyld and Wright (2001)—in which Jurassic rocks of the Blue Mountains region accumulated in a colli-sional basin adjacent to a large Jurassic orogenic belt in western Nevada (Luning-Fencemaker thrust belt) (Dorsey and LaMaskin, 2007, 2008; LaMaskin et al., 2008a, 2009).

SAMPLE COLLECTION AND ANALYTICAL PROCEDURES

Sandstone Petrography

We collected sandstone samples for petro-graphic analysis to permit comparison with previously well-documented shifts in sandstone composition in Mesozoic rocks of the John Day region (Dickinson et al., 1979; see previous summary). Sandstone samples were analyzed to assess the age of the change from outboard Baker terrane sources to inboard sources, and the relationship between sandstone petrofacies and detrital zircon ages. In the John Day region, we collected sandstones from the Fields Creek Formation and Keller Creek Shale (Aldrich Mountains Group). In eastern Oregon–western Idaho, we collected sandstone samples from multiple locations in the Weatherby Formation flysch unit. Point-counting parameters are listed in Table 1, and a description of procedures for sandstone petrography is presented in the GSA Data Repository.1

Detrital Zircon Analysis

We collected 5 to 10 kg samples of sandstone from biostratigraphically dated horizons in both the John Day region (“Izee terrane” of Silberling et al., 1984) and eastern Oregon–western Idaho (“Olds Ferry terrane” of Silberling et al., 1984). Sampled Triassic rocks include the Begg and Brisbois Members of the Vester Formation and the Fields Creek Formation in the John Day re-

gion (Figs. 3 and 4; Table 2). Numerous attempts to extract zircons from Triassic sandstones of the Huntington Formation in eastern Oregon were unsuccessful. We sampled Jurassic rocks includ-ing the Keller Creek Shale and the Hyde, Snow-shoe, and Lonesome Formations in the John Day region, and the Weatherby Formation in eastern Oregon. U-Pb data for 10 samples were obtained by laser ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS) at Washington State University following the method of Chang et al. (2006). U-Pb data for one additional sample was analyzed at Stanford University on the joint U.S. Geological Survey (USGS)–Stanford sen-sitive high-resolution ion microprobe–reverse geometry (SHRIMP-RG). A description of U-Pb analytical procedures is presented in the GSA Data Repository (see footnote 1).

RESULTS


Raw point-count data from sandstone modal analysis and detailed petrofacies descriptions are provided in the GSA Data Repository (see footnote 1), and recalculated parameters are presented in Table 3. Examples of sandstone grains in thin section are shown in Figure 5, and Figure 6 illustrates ternary plots of sandstone detrital modes.

Fields Creek FormationModal analysis of the Late Triassic Fields

Creek Formation (John Day region) suggests two distinct petrofacies: volcaniclastic and

1GSA Data Repository item 2011188, (1) descrip-tion of petrographic procedures, (2) description of U-Pb analytical procedures, (3) Table DR1—raw petro graphic point-count data, and (4) Table DR2— U-Pb analytical data tables, is available at http://www.geosociety.org/pubs/ft2011.htm or by request to [email protected].

TABLE 1. SUMMARY OF PARAMETERS FOR SANDSTONE MODAL ANALYSIS

Quartz (Q)Qm = Monocrystalline quartzQp = Polycrystalline quartzCh = Chert

Feldspar (F)P = PlagioclaseK = Potassium feldspar

Lithic fragments (L)Ls = Lithic sedimentary

Lsm = Shale/mudstoneLsa = Argillite Lssi = SiltstoneLsst = Sandstone (traditional method only)

Lm = Lithic metamorphicLmp = PhylliteLms = SlateLma = Quartz-mica aggregateLmt = Quartz-mica tectonite

Lv = Lithic volcanicLvmi = MicroliticLvm = LathworkLvf = FelsiticLvv = Vitric

Recalculated parameters:Q/F/L = Q(Qm + Qp + Ch)/F(P + K)/L(Ls + Lm + Lv)

Qm/F/Lt = Qm/F(P + K)/Lt(Ls + Lm + Lv + Qp + Ch)

Qp/Lv/Lsm = Qp(Qp + Ch)/Lv/Lsm([Ls – Ch] + Lm)



LaMaskin et al.


quartzolithic (Fig. 6). Volcaniclastic sandstones contain abundant plagioclase and volcanic lithic fragments. They plot in the transitional arc field on Q-F-L and Qm-F-Lt ternary diagrams and in, or close to, the magmatic arc field on a Qp-Lv-Lsm diagram (Fig. 6). These samples contain greater amounts of quartz and feldspar and more sedimentary and metamorphic lithic fragments than “Jurassic volcaniclastics” in the overlying Mowich Group and Snowshoe For-mation (Dickinson et al., 1979), suggesting a distinct provenance for Triassic volcaniclastic sediments of the Fields Creek Formation.

Quartzolithic sandstones are low in feld-spar and volcaniclastic content and contain abundant lithic fragments of principally sedimentary and metamorphic composition. Sedimentary lithic fragments consist of shale-mudstone and argillite (Fig. 5A). Low-grade meta-sandstone and meta-graywacke grains (e.g., Fig. 5B) are also present. Metamorphic lithic fragments include abundant phyllite-schist, quartz-mica tectonite (Fig. 5C), and quartz-mica aggregate grains with subordinate quantities of slate. Grains of silicic plutonic

rocks that display distinctive granophyric tex-tures are also present (Fig. 5D).

Quartzolithic sandstones of the Fields Creek Formation plot in recycled orogen fields on Q-F-L, Qm-F-Lt, and Qp-Lvm-Lsm diagrams (Fig. 6), consistent with derivation from the uplifted Baker terrane accretionary subduction complex as suggested in previous studies (Dick-inson and Thayer, 1978; Blome et al., 1986; Dorsey and LaMaskin, 2007). Although Dickin-son et al. (1979) noted the presence of chert-rich, mélange-derived detritus in the Fields Creek Formation, here we document that the quartzo-lithic petrofacies in the Fields Creek Formation is uniquely enriched in sandstone and metamor-phic lithic fragments that range from slate to quartz-mica tectonite (Figs. 5A, 5B, 5C, and 6).

Keller Creek Shale and Weatherby FormationVolcaniclastic sandstones in the Lower Juras-

sic Keller Creek Shale (John Day region) and Middle Jurassic Weatherby Formation (eastern Oregon–western Idaho) are characterized by variable mixtures of feldspar (Fig. 5E) and vol-canic lithic fragments. Observed sedimentary

lithic fragments are limited to shale and mud-stone. In addition to these framework constitu-ents, detrital pyroxene grains form 6%–10% of total framework and accessory grains (Fig. 5F). Sandstones in the Keller Creek Shale and Weatherby Formation plot in the magmatic arc field on Qp-Lv-Lsm plots (Fig. 6A) and tran-sitional to undissected arc fields on Q-F-L and Qm-F-Lt plots (Figs. 6B and 6C). These sam-ples plot very close to other Jurassic vol cani-clastics as reported by Dickinson et al. (1979). Our limited analysis suggests that selected ho-rizons in the Weatherby Formation may contain either higher quartz or higher volcanic lithic content than Jurassic volcaniclastics of the John Day region, but sandstones from both regions have very similar modal compositions.


Complete U-Pb zircon data tables are pro-vided in the accompanying GSA Data Reposi-tory (see footnote 1). Data are illustrated on Tera-Wasserburg plots in Figure 7, and relative probability plots and histograms are provided in Figure 8. Reported ages are based on 206Pb/238U for grains younger than ca. 1000–1200 Ma and 207Pb/206Pb for grains older than ca. 1000–1200 Ma. Results are summarized next.

John Day Region: Late Triassic Samples of Megasequence 1

Detrital zircon age-probability distributions from the Begg Member (sample 06139) and Brisbois Member (sample 06004) of the Vester Formation include very few Mesozoic-age zir-con grains (Figs. 8 and 9). These samples contain abundant Devonian-, Mississippian-, Pennsyl-vanian-, and Permian-age grains and have

TABLE 2. SAMPLE LOCATION INFORMATION

gnihtroN*gnitsaEnoitamroF.onelpmaS04064 Weatherby Formation, Jet Creek Member 0480251 491798206004 Vester Formation, Brisbois Member 0305333 4890634

14021944417130noitamroFkeerCsdleiF8116022749844281230noitamroFeohswonS5316068379840222530elahSkeerCrelleK73160

06139 Vester Formation, Begg Member 0289898 488397207398843344130noitamroFedyH2516026652945942740noitamroFybrehtaeW0126081387842091130noitamroFemosenoL5107017111946372740noitamroFybrehtaeW3307084408841911130noitamroFemosenoL7-EEZI53977847881130noitamroFemosenoL9-EEZI

*UTM Datum NAD 27 CONUS, UTM zone 11.

TABLE 3. RECALCULATED MODAL POINT-COUNT DATA FOR SANDSTONE SAMPLES OF THE BLUE MOUNTAINS PROVINCE, OREGON

Q-F-L (%) Qm-F-Lt (%) Qp-Lv-Lsm (%) Lv-Ls-Lm (%)

mLsLvLmsLvLpQtLFmQLFQlatoT.onelpmaSnoitamroFFields Creek Formation 06122 401 40 7 53 23 7 70 25 9 67 12 41 48

06123 446 43 4 53 24 4 72 26 8 65 11 45 4306009 380 46 2 52 19 2 79 34 15 52 22 28 5006118* 429 21 45 34 10 45 45 25 59 16 79 21 006129 392 19 58 24 9 58 33 28 55 17 77 22 1

Keller Creek Shale 06131 403 5 46 49 3 46 51 3 89 9 91 8 106130 406 5 42 53 3 42 56 4 92 4 96 4 006133 412 3 47 50 2 47 51 2 97 1 99 1 006137* 408 6 43 51 4 43 53 4 92 4 96 4 0

Weatherby Formation Lower Flysch07033e* 406 4 20 76 4 20 76 0 98 2 98 2 007035 432 13 19 68 12 19 70 2 97 1 99 1 0

Main Flysch07038 407 4 32 65 2 32 66 2 97 1 99 1 007039 403 5 17 78 2 17 81 4 95 1 99 1 007040 422 2 26 72 2 26 72 1 99 0 100 0 007044 439 4 18 78 3 18 79 2 98 0 100 0 006210† 399 5 26 70 4 26 70 1 98 1 99 1 007042 404 19 18 63 2 18 79 21 79 0 100 0 0

*Detrital zircon sample.





A

0.4 mm

C

0.4 mm

E

0.4 mm

F

0.2 mm

D

0.4 mm

B

0.5 mm

Figure 5. Photomicrographs of key framework grain types in Blue Mountains Province sandstone samples. All photomicro-graphs were taken in cross-polarized light. (A) Lithic fragment of silty argillite to slate from quartzolithic petrofacies of Fields Creek Formation. Note selective internal calcite replacement and breakdown to form pseudomatrix along grain edges. (B) Lithic fragment of low-grade metagraywacke in calcite-cemented sandstone from quartzolithic petrofacies of the Fields Creek For-mation. Phyllosilicate minerals replace clay-rich matrix within detrital grain. (C) Lithic grain of quartz-mica tectonite from quartzolithic petrofacies of Fields Creek Formation. Note strong planar fabric of elongated quartz and aligned phyllosilicate minerals. (D) Lithic grain of plutonic origin displaying distinctive granophyric texture from volcaniclastic petrofacies of the Fields Creek Formation. (E) Typical view of volcaniclastic petrofacies of Keller Creek Shale. Note well-rounded plagioclase grains, lithic grains displaying lathwork texture, and abundant pseudomatrix. (F) Well-rounded detrital pyroxene grain from the Weatherby Formation.



LaMaskin et al.


abundant Precambrian age peaks in the late Paleo-proterozoic (ca. 2.2–1.6 Ga) and Late Archean (ca. 2.7–2.5 Ga). The Fields Creek Formation sample (06118) has predominantly Permian–Triassic (ca. 280–242 Ma) and Silurian–Devonian ages (ca. 436–385 Ma), with fewer Precambrian grains from Late Paleoproterozoic (ca. 1.9–1.6 Ga) to Mesoproterozoic (ca. 1.4–1.0 Ga).

John Day Region: Early Jurassic Samples of Megasequence 1

Sandstone in the Keller Creek Shale (sample 06137) is characterized by a single major distri-bution of Late Triassic to Early Jurassic grains (ca. 218–181 Ma; peak at 195 Ma; Figs. 8 and 9) and fewer Mesoproterozoic (ca. 1.5–1.0 Ma) and Paleoproterozoic (ca. 1.9–1.7 Ga) grains.

John Day Region: Middle and Early Late Jurassic Samples of Megasequence 2

All zircons in the Hyde Formation of the Mowich Group (sample 06152) are Meso-zoic, with a unimodal age distribution from 199 to 172 Ma and a peak at 180 Ma. Our samples from the Snowshoe Formation (06135) and from the Lonesome Formation (07016, IZEE-7, and IZEE-9) have similar age-probability distributions (Figs. 8 and 9). These samples have zircons with complex, multimodal distributions in the Late Triassic to early Late Jurassic (ca. 217–159 Ma). The Lonesome Formation has a relatively continu-ous distribution of Paleozoic detrital zircon grains. Precambrian grains include abundant Neo protero zoic (ca. 675–576 Ma) and Meso-

proterozoic ages (ca. 1.5–1.0 Ga) with lesser amounts of late Paleoproterozoic (ca. 1.9–1.8 Ga) and few Archean grains.

Eastern Oregon: Early to Middle Jurassic Samples of Megasequence 2

Samples from the basal Jet Creek Member of the Weatherby Formation (sample 04064) and lower part of the overlying flysch member (sample 07033) contain zircons with a range of ages from Late Triassic to Early Jurassic (ca. 225–190 Ma) with a major peak at ca. 200 Ma (Figs. 8 and 9). Both of these samples are void of Precambrian or Paleozoic zircons. In sample 07033, three detrital zircon grains define an addi-tional age peak at ca. 178 Ma. One sample from the upper flysch of the Weatherby Formation

LF

RO

TC

CI

dissectedarc

transitionalarc

F Lt

TC QR

M

Qp

Jurassic volcaniclastic

units

Q Qm

Lvm Lsm

A

B C

basementuplift

dissectedarc

transitionalarc

undissectedarc

basementuplift

undissectedarc

transitionalrecycled

lithicrecycled

magmatic arc

recycled orogen

EXPLANATION

Fields Creek Fm.

Keller Creek Shale

Weatherby Fm.

Vester Fm.

Jurassic volcaniclastic units:Hyde and Snowshoe fms.

Lonesome Fm.

Data from DICKINSON et al., 1979

THIS STUDY

recycled orogen

subduction complex

50% 50%

Lvm

Figure 6. Ternary diagrams illustrating sandstone detrital modes for the Fields Creek Formation, Keller Creek Shale, and Weatherby Formation. (A) Qp-Lvm-Lsm. Inset is a close-up of the Lsm apex to show detail. (B) Q-F-L. (C) Qm-F-Lt. Tectonic setting classification fields are from Dickinson and Suczek (1979); Dickinson et al. (1983); and Dickinson (1985). Also shown are results taken graphically from Dickinson et al. (1979) for the Vester Formation, “Jurassic volcaniclastic” units, and the Lonesome Formation.





(sample 06210) yielded only Late Triassic to Middle Jurassic ages (ca. 214–169 Ma), with two dominant peaks evident at ca. 178 and ca. 196 Ma (Figs. 8 and 9). Five zircons from this sample have pre-Mesozoic ages.

DISCUSSION


In Fields Creek Formation samples, the pres-ence of abundant sedimentary lithic fragments in addition to volcanic detritus is interpreted to represent a “relict petrofacies,” where an arc system is no longer active but is still contribut-ing detritus to the basin (cf. Graham et al., 1993; Critelli and Ingersoll, 1995). Our new U-Pb data support this interpretation because the associ-ated sandstone sample does not contain zircons with U-Pb ages that overlap the well-established biostratigraphic age of the Fields Creek Forma-tion (Fig. 9; and see following). We therefore conclude that there was not an active arc sup-plying detritus to this part of the basin during Late Triassic time.

Notable granophyric plutonic grains (Fig. 5D) in the Fields Creek Formation are clearly derived from granophyric plutonic rocks that are located immediately to the northwest in the Baker terrane (Carpenter and Walker, 1992) and are also observed as olistostromal slide blocks in basal parts of the Fields Creek Formation (Thayer and Brown, 1966). Permian U-Pb zir-con ages of these Baker terrane plutonic blocks (Carpenter and Walker, 1992) are in excellent agreement with detrital zircon ages from the Fields Creek Formation (see following).

The presence of two distinct petrofacies in the Fields Creek Formation—volcaniclastic and quartzolithic (Fig. 6)—suggests a recycled orogenic source for this unit. Modern sediments in the southern Aegean Sea are composed of similar mixtures of volcaniclastic and quartzo-lithic sands. In this setting, a wide ancient oro-genic belt borders an active forearc and supplies two types of sediment to local basins (Saccani, 1987). Additionally, in the modern Apennine backarc region, source-area variability along orogenic strike leads to deposition of sand with either magmatic or orogenic provenance (e.g., Garzanti et al., 2000, 2007). Notably, relict quartzolithic-volcaniclastic petrofacies are also documented in Upper Paleozoic to Upper Trias-sic sandstones in California and Nevada (Dick-inson and Gehrels, 2000). This may suggest the presence of a recycled orogenic source area (Baker terrane and lateral equivalents) along a significant portion of the Cordilleran margin during Late Triassic time.

In the Keller Creek Shale and Weatherby For-mation, distinctive well-rounded to subangu-

lar detrital pyroxene and abundant intact lithic fragments suggest relatively short transport dis-tances for volcanic detritus. A low proportion of sedimentary or metamorphic lithic fragments suggests an active arc setting (cf. Graham et al., 1993; Critelli and Ingersoll, 1995).


Outboard versus Inboard Sediment SourcesIn this study, we benefit from preexisting

paleon tologic, sandstone petrographic, and paleo current data that provide useful constraints on sediment provenance (i.e., Dickinson and Thayer, 1978; Dickinson et al., 1979; Blome et al., 1986). A major source area change in the John Day region that is documented with sand-stone petrofacies (Dickinson et al., 1979) is also recorded in detrital zircon age distributions. Chert- and metamorphic lithic-rich Late Trias-sic samples likely derived from outboard sources (i.e., the offshore Baker terrane) are dominated by Precambrian and Paleozoic ages (96%–100%; Fig. 10A) and include negligible amounts of Mesozoic-age detrital zircon grains (i.e., 0%–4%; Figs. 9 and 10A). Precambrian grains in these Late Triassic sediments are mostly late Paleoproterozoic and Archean (ca. 2.7–1.8 Ga), typical of northwestern Laurentian basement ages (cf. Gehrels et al., 1995, 2000) (Figs. 9 and 10B). In contrast, Jurassic volcaniclastic samples derived from inboard sources contain at least half Mesozoic-age detrital zircon grains (i.e., 52%–100%; Figs. 9, 10A, and 11). Pre cambrian grains in the Jurassic samples are mostly Late Paleoproterozoic to Neoproterozoic (ca. 2.0 Ga to 600 Ma), which are commonly considered typical of eastern and southwestern Laurentian basement ages (Figs. 9 and 10B). This suggests a change in provenance and an increase in local or regional magmatism from Late Triassic to Early Jurassic time (cf. Brown and Thayer, 1977).

At face value, the observed change from typical northwestern to eastern-southwestern Laurentian-type zircon ages is consistent with models for southward displacement of the Blue Mountains relative to North America during Triassic through Early Cretaceous time (i.e., Avé Lallemant and Oldow, 1988) and is in con-flict with faunal evidence that suggests progres-sive northward transport of the Blue Mountains Province (i.e., Pessagno and Blome, 1986; Pessagno, 2006). However, well-documented sandstone detrital modes show that Triassic deposits have a provenance distinct from over-lying Jurassic deposits (Dickinson and Thayer, 1978; Dickinson, 1979; Dickinson et al., 1979). Thus, the change in detrital zircon ages is more directly related to a change from outboard to in-board sources and does not necessarily reflect

southward translation through time. In this case, a priori knowledge of sediment sources from sandstone petrofacies analysis is critical to the interpretation of associated detrital zircon age distributions. This highlights the need to inter-pret detrital zircon age distributions in the con-text of sandstone petrography.

Late Triassic Samples: Outboard ProvenanceDetrital zircon ages in the Vester and Fields

Creek formations characterize the outboard Baker terrane accretionary subduction com-plex source area and suggest two distinct de-trital zircon sources: one that supplied middle to late Paleozoic, late Paleoproterozoic, and late Archean zircons to the Vester Formation and another that supplied Permian–Triassic, Silurian–Devonian, Mesoproterozoic, and late Paleoproterozoic zircons to the Fields Creek Formation (Figs. 8, 9, and 10). Existing Ar/Ar and U-Pb ages for pre-Jurassic rocks from the Baker terrane, however, document only Late Triassic to Permian plutonic ages, even though sedimentary rocks as old as Middle Devonian are present (Savage and Amundson, 1979; Avé Lallemant et al., 1980; Morris and Wardlaw, 1986; Walker, 1986, 1995; Blome and Nestell, 1991; Carpenter and Walker, 1992).

The presence of late Paleozoic, late Paleo-proterozoic, and late Archean grains in Trias-sic sandstone of the Vester Formation suggests a Baker terrane subduction-accretionary com-plex source analogous to Paleozoic subduction-accretionary complexes of the Eastern Klamath and Northern Sierra terranes, which bear simi-lar detrital zircon age distributions. For exam-ple, the Lang-Duncan-Culbertson allochthons of the Shoo Fly complex (Northern Sierra terrane) contain abundant late Paleo protero-zoic and late Archean detrital zircon grains (Harding et al., 2000) and are intruded by Late Devonian plutons (i.e., Bowman Lake suite, ca. 378–370 Ma; Saleeby et al., 1987; Hanson et al., 1988; Sharp, 1988).

The Upper Triassic Fields Creek Formation appears to contain a “transitional” detrital zir-con age distribution, with abundant Paleozoic ages similar to underlying samples, but with Precambrian ages rich in Mesoproterozoic and Neoproterozoic zircons similar to younger Jurassic samples (Figs. 8, 9, and 10). Detrital zircon and petrographic data presented here thus record a shift in provenance from the Vester to Fields Creek formations (Figs. 8, 9, and 10B). Significant differences in both sandstone detrital modes and detrital zircon signatures suggest that detritus in the Fields Creek Formation was not produced only by erosion and reworking of the Vester Formation, as suggested by Dickin-son and Thayer (1978).



LaMaskin et al.


207 P

b/2

06P

b20

7 Pb

/206

Pb

207 P

b/2

06P

b20

7 Pb

/206

Pb

200600

1000

0.04

0.08

0.12

0.16

0.20

0.24

0 10 20 30 40 50

1000600

200

0.04

0.08

0.12

0.16

0.20

0.24

0 10 20 30 40 50

200

1000600 200

0.04

0.08

0.12

0.16

0.20

0.24

0 10 20 30 40 50

1000600

0.04

0.08

0.12

0.16

0.20

0.24

0 10 20 30 40 50

200

230

0.04

0.05

0.06

0.07

0.08

25 27 29 31 33 35 37 39

1000

6000.04

0.08

0.12

0.16

0.20

0.24

0.04

0.08

0.12

0.16

0.20

0.24

0 10 20 30 40 50

1000600

0.04

0.08

0.12

0.16

0.20

0.24

0 10 20 30 40 50

238U/206Pb

1000600

0 10 20 30 40 500.044

0.048

0.052

0.056

0.060

25 27 29 31 33 35

0.05

0.06

0.07

0.08

22 26 30 34 38

Keller Creek Fm.Sample 06137

n = 128

Hyde Fm.Sample 06152

n = 88

Weatherby Fm.Jet Creek Mbr.Sample 04064

n = 47

Weatherby Fm.Lower FlyschSample 07033

n = 48

Vester Fm.Brisbois Mbr.Sample 06004

n = 112

Fields Creek Fm.Sample 06118

n = 122

Vester Fm.Begg Mbr.

Sample 06139n = 105

170190210

200200

200

250 230 210 190 170

240 230 220 210 200 190 180210 190 170

400 400400

Snowshoe Fm.Sample 06135

n = 126

Lonesome Fm.Sample 07016

n = 146

Weatherby Fm.Upper FlyschSample 06210

n = 121

238U/206Pb 238U/206Pb

0.04

0.08

0.12

0.16

0.20

0.24

0 10 20 30 40 50

Lonesome Fm.Samples IZEE-7

and IZEE-9N = 2; n = 109

Depo. age =ca. 225 Ma











Figure 7. Tera-Wasserburg Pb-Pb/U-Pb concordia plots for detrital zircons from the Blue Mountains Province. Errors are shown at the 2s level. Data shown have not been corrected for common Pb. Shadowed insets show additional detail for Paleozoic and Mesozoic zircon grains. Samples containing Precambrian-age zircon grains are plotted at the same scale. Samples 06152, 04064, and 07033 are scaled to fit.





0 500 1000 1500 2000 2500 3000

Keller Creek Fm.Sample 06137

n = 128

195

1075 ~1400

1850

012345

1000 1200 1400 1600 1800

n = 21

0 500 1000 1500 2000 2500 3000

n = 116180

196

0

5

10

15

20

25

30

35

160 180 200 220

0 500 1000 1500 2000 2500 3000

Lonesome Fm.Sample 07016

n = 146

n = 68

135

200 300 400 500 600 700

13

900 1100 1300150017001900

n = 30

n = 430369

1215

160 180 200 220

162

181189

285 422 545 635577

1540 174010301140 1270

0 500 1000 1500 2000 2500 3000

Snowshoe Fm.Sample 06135

n = 126

178

1457 18401150 1288

1040

n = 33

0246

700 1100 1500 1900

Hyde Fm.Sample 06152

n = 88180

187

195

0

5

10

15

20

25

160 170 180 190 200 210 220 230 240 250

Weatherby Fm.Jet Creek Mbr.Sample 04064

n = 47

198

204

212

224

0

2

4

6

8

10

190 200 210 220 230 240 250

190

0 500 1000 1500 2000 2500 3000

198

219

178

0

2

4

6

8

10

160 180 200 220 240 260

n = 47

Age (Ma)

Age (Ma)

Age (Ma)

Age (Ma)

Age (Ma)

Age (Ma) Age (Ma)

0 500 1000 1500 2000 2500 3000

310

274

223

389

435 1850

1752 -1987

2525 -2718

0 500 1000 1500 2000 2500 3000

Fields Creek Fm.Sample 06118

n = 122

264

423

1014 -1364

1615

17801867

1048

0123456

1000 1200 1400 1600 1800

1657

n = 32

0 500 1000 1500 2000 2500 3000

321

373

1827

1878

1995

2209-2381

2546-2697

Age (Ma) Age (Ma) Age (Ma)

1366

1523 16731632

02468

10

300 380 460

n = 22

321

373

1665

547

878

Vester Fm.Begg Mbr.

Sample 06139n = 105

168178

190

207

n = 81

02468

1012

160 180 200 220

195

~654

Weatherby Fm.Lower FlyschSample 07033

n = 48

Weatherby Fm.Upper FlyschSample 06210

n = 121

0

4

8

12

240 320 400 480

n = 72

223

274

310

389

Vester Fm.Brisbois Mbr.Sample 06004

n = 112~435

0 500 1000 1500 2000 2500 3000

Lonesome Fm.Sample IZEE-7

& IZEE-9N=2;

n = 109

Age (Ma)

048

1216

160 180 200 220

n = 60168175

182 208

01234

200 300 400 500 600

n = 19244 363415-

444516-583 606-

632

900 1100 1300 1500 1700 19000246

n = 211037-10941150

1750

Figure 8. Relative probability plots and histograms for detrital zircons from the Blue Mountains Province. Curves represent the summation of individual detrital zircon ages and associated 2s Gaussian errors; associated y-axes represent relative probability. Histograms are based on individual detrital zircon grain ages and do not incorporate errors; associated y-axes represent number of grains in a given age bin. Shadowed insets show additional detail. Samples containing Precambrian-age zircon grains are plotted at the same scale. Samples 06152 and 04064 are scaled to fit.



LaMaskin et al.


Evidence that detritus in the Fields Creek Formation was produced by reworking of older deposits in the Baker terrane includes an abun-dance of Permian–Triassic detrital zircon grains (ca. 280–242 Ma) that closely match ages from granophyric plutonic blocks found in the Baker terrane (ca. 272–236 Ma; published range of 206Pb/238U ages on multigrain zircon fractions in Carpenter and Walker, 1992). In addition, the Fields Creek Formation has a well-established Late Triassic radiolarian age (early Norian to late middle Norian; ca. 216–206 Ma; Blome et al., 1986; Yeh, 1989), but the youngest detrital zircon grains are Middle Triassic, representing a lag time of nearly 30 m.y. Together with the petrographic data presented previously, this in-

dicates that the Fields Creek Formation detritus was not derived from an active-arc setting such as the inboard Cordilleran arc.

The presence of abundant metamorphic and sedimentary framework grains suggests a rela-tively short transport distance for detritus of the Fields Creek Formation. A potential source area is the Deer Creek Phyllite (Burnt River Schist subterrane of the Baker terrane), a unit that ap-pears to be intruded by the ca. 230 Ma Blue Spring Gulch pluton (Ashley, 1995; Walker, 1995; sample BRC79-1). Comparable detrital U-Pb zircon ages are not present in our sample from the Fields Creek Formation, suggesting a source other than the Burnt River Schist. Little-studied schistose rocks are also present at Iron-

side Mountain to the east of the John Day region (Hooper et al., 1995). Further analysis of the Burnt River Schist and Ironside Mountain areas may yield insights into the source of Fields Creek Formation detritus.

Exposures of Paleozoic schist, graywacke, and sandstone in the Eastern Klamath terrane represent a possible source-area lithology and contain an appropriate detrital zircon age distri-bution that includes a ca. 420 Ma age peak, ca. 600–500 Ma Neoproterozoic-age grains, and Precambrian ages dominated by 2.0–1.0 Ga grains (Fig. 12; Gehrels and Miller, 2000; Grove et al., 2008). This suggests either deriva-tion from metasedimentary rocks of the East-ern Klamath terrane or more likely indicates

Grains <600 Ma Grains >600 Ma

n = 83

n = 39

n = 37

n = 24

n = 0

n = 39

n = 77

n = 22

n = 73

n = 85

n = 106

n = 88

n = 87

n = 178

Lonesome Fm.

Snowshoe Fm.

Hyde Fm.

Keller Creek Fm.

Fields CreekFm.

Vester Fm.,Brisbois Mbr.

Vester Fm., Begg Mbr.

ca.180 Ma Toarcian

ca.172 MaAalenian

ca.165 MaBathonian

ca.159 MaOxfordian

600

800

1000

1200

1400

1600

1800

2000

2200

2400

2600

2800

3000

3200

3400

100

150

200

250

300

350

400

450

500

550

600

ca. 210 Ma Norian

ca. 225 Ma Carnian

ca. 217 MaCarnian

Late Triassic

EarlyJurassic

Middle Jurassic

earlyLate

Jurassic

Age (Ma) Age (Ma)

Depositional age

Neo- Meso- Paleo-Archean

Proterozoic

OSDMPJ CPTR

PaleozoicMesozoic

Angular unconformity

Depo.Age (typ.)

John Day Region:

Figure 9. Detrital zircon age-probability distributions from the John Day region shown for ages younger than 600 Ma and ages older than 600 Ma for each sample. Samples are plotted on the y-axis in depositional order.





the presence of rocks in the Baker terrane that are similar to those of the Eastern Klamath ter-rane. This Baker terrane source area has either not yet been adequately characterized or is con-cealed beneath Miocene-age Columbia River Basalts. Petrographic and detrital zircon data therefore suggest that the Fields Creek Forma-tion most likely was derived from an Eastern Klamath terrane–type source located in the Baker terrane.

Numerous plausible scenarios exist for Late Triassic erosion, transport, and deposition of detrital zircon grains in Blue Mountains ba-sins. First, the grains may have been eroded from crystalline sources in the Baker terrane that are not currently exposed, have yet to be

recognized, or have been tectonically removed since Triassic time. Second, they may have been reworked from Paleozoic clastic rocks in the Baker terrane. Third, grains in Triassic rocks of the Blue Mountains may have been reworked from Paleozoic clastic rocks in the Eastern Klamath–Northern Sierra terranes. Detrital zir-con age distributions from subduction-accretion complexes in the Eastern Klamath and Northern Sierra terranes contain two distinct age distribu-tions similar to the two Baker-terrane sources documented here (Gehrels and Miller, 2000; Harding et al., 2000; Grove et al., 2008). In the third scenario, detrital zircon grains eroded from exposed sources to the south must have been funneled into the Triassic trench, trans-

ferred to the Baker terrane accretionary prism (via underplating and/or offscraping), uplifted, eroded, and subsequently deposited in Triassic basins in the John Day region. Well-constrained sandstone and faunal provenance linkages to the immediately adjacent Baker terrane (Dickinson et al., 1979; Blome et al., 1986) suggest that the detrital zircon sources are present in exposed Paleozoic clastic rocks of the Baker terrane (e.g., Alexander and Schwartz, 2009).

Implications of Triassic Detrital Zircon Sources

The Paleoproterozoic- and Archean-domi-nated Precambrian ages documented here for the Late Triassic Vester Formation represent a

5

66

60

21

52

64

100

80

2

4

0% 20% 40% 60% 80% 100% 0% 20% 40% 60% 80% 100%

Relative Proportion of All Ages in Sample

Relative Proportion ofPrecambrian Ages in Sample

Mesozoic Paleozoic Precambrian

30

18

4

10

49

33

38

13

5

5

4

8

23

14

Archean

Lonesome Fm.

Snowshoe Fm.

Hyde Fm.

Keller Creek Fm.

Fields Creek Fm.

Vester Fm., Brisbois Mbr.

Vester Fm., Begg Mbr.

44 5

Late Triassic

Early Jurassic

Middle Jurassic

earlyLate

Jurassic

36

79

32

2 18

31

Neo Meso Paleo

Proterozoic

199.6±0.6

175.6±2.0

161.2±4.0

Angular unconformity

28

58

44

63

78

3

14 34 21

A

EXPLANATION

B

Depositional age

Sampled formation

2

Figure 10. Plots illustrating proportion of detrital zircon ages based on major divisions of the geologic time scale. Y-axis is approximate depositional age and sampled formation. (A) Percentage of the total sample that is represented by Mesozoic, Paleozoic, and/or Precambrian ages. (B) Percentage of the Precambrian portion of the sample that is represented by Neoproterozoic, Mesoproterozoic, Paleoproterozoic, and/or Archean ages.



LaMaskin et al.


“Peace River Arch”–type signal, commonly in-terpreted to represent basement ages in north-western Laurentia (e.g., Gehrels et al., 1995; Gehrels, 2000). This Paleoproterozoic–Archean age distribution is found in detrital zircon suites in numerous Cordilleran terranes from Cali-fornia to Alaska and is especially common in Paleozoic subduction-accretionary complexes (Gehrels and Kapp, 1998; Harding et al., 2000; Spurlin et al., 2000; Scherer, 2006; Brown and Gehrels, 2007). Precambrian ages in the Vester Formation and its Baker-terrane source therefore cannot be uniquely tied to a particu-lar source area. Rather, continuity with detrital suites in other Cordilleran accretionary subduc-tion complexes reinforces the interpretation that the Baker terrane is part of the late Paleozoic to Mesozoic paired accretionary complex and fringing-arc system of western North America (e.g., Wright, 1982; Miller, 1987; Miller et al., 1992; Gehrels et al., 2000; Dickinson, 2000). This interpretation implies multiple sedimen-tary recycling episodes of zircon grains that were ultimately derived from northwestern Lau-rentian basement rocks.

An alternative explanation, based on a re-cent model for the tectonic evolution of western North America (Wright and Wyld, 2006; Grove et al., 2008), proposes tectonic dispersal of originally peri-Gondwanan arc fragments from the southern Laurentian margin in Devonian time. According to this model, these “Alexan-der terrane–type” arc segments were accreted to western North America in mid-Paleozoic time as parts of the Eastern Klamath and Sierra Ne-vadan terranes and the Roberts Mountain and Golconda allochthons (Wright and Wyld, 2006; Grove et al., 2008). These blocks of allochtho-nous arc crust may have acted as basement for future arc growth in the western United States, parts of which rifted from the western Lauren-tian margin to form the offshore segment of the Permian–Triassic Cordilleran arc. Sedimentary rocks of these arc fragments contain two distinct detrital zircon signatures: Archean- to Paleo-proterozoic-enriched, and Mesoproterozoic- to Neoproterozoic-enriched (Wright and Wyld, 2006). This interpretation implies multiple sedi-mentary recycling episodes of zircon grains that were ultimately derived from both Gondwanan and eastern Laurentian basement rocks.

Regardless of the ultimate origin of detrital zircons, our data strongly suggest that the Baker terrane source area has genetic links to the nearby Eastern Klamath and Northern Sierra terranes, either as an analogous allochthonous crustal fragment (further extending the geo-graphic extent of Alexander-type crust of the “Cordilleran” Paleozoic arc; i.e., Wright and Wyld, 2006), or via a sediment-transport and re-

cycling link. Future characterization of detrital zircon age distributions in the Klamath Moun-tains and Baker terrane is needed to clarify prov-enance relationships between these regions.

Jurassic Samples: Inboard ProvenanceDetrital zircon age distributions in Jurassic

deposits indicate derivation from inboard source areas that were dominated by volcanic rocks, and they provide a record of Jurassic magma-tism in the Cordilleran arc. Previous correla-tions of Jurassic turbidites from the John Day region to eastern Oregon (Dickinson, 1979; Imlay, 1986; Pessagno and Blome, 1986; Avé Lallemant, 1995; Vallier, 1995; Dorsey and LaMaskin , 2007, 2008) are confirmed here by similar detrital zircon age distributions (Fig. 11). Early Jurassic samples from both the John Day region and eastern Oregon (Huntington area), as shown in Figure 11, contain a dominant signal of Late Triassic through Early Jurassic magma-tism (ca. 210–185 Ma; mode at 198–195 Ma). The youngest Early Jurassic sample (Weath-erby Formation, Lower Flysch) also contains three zircons ca. 178 Ma, suggesting onset of a subsequent Early to Middle Jurassic magmatic pulse. The subsequent pulse is well represented in succeeding Middle Jurassic samples from both the John Day region and eastern Oregon by age modes at ca. 178 Ma (Fig. 11). Finally, the Snowshoe and Lonesome formation samples also contain abundant Middle Jurassic detrital zircon grains (ca. 170–159 Ma).

These detrital zircon data suggest a distinc-tive pattern of neo- and paleomagmatic sources in an active-arc setting, where sandstone de-trital modes can only identify a volcaniclastic petrofacies. A significant phase of Late Triassic magmatic activity in the Olds Ferry arc (Brooks et al., 1976; Brooks, 1979; Walker, 1986; Lund, 2004; LaMaskin, 2008; Unruh et al., 2008) is represented by only a minor component of the age distributions (Fig. 11). Lower Jurassic samples are dominated by ages from ca. 198 to 195 Ma, and Middle to early Late Jurassic samples are dominated by ages from ca. 180 to 175 Ma and ca. 168 Ma. Thus, in succes-sively younger samples, older ages become less prominent and are replaced by progressively younger ages. These observations suggest that the majority of detrital zircon grains are from neovolcanic sources that blanketed local drain-age basins. In this scenario, underlying older paleo volcanic material was only partially ex-posed, and “young” magmatic detritus domi-nates the detrital zircon age suite.

Overall, detrital zircon age distributions in Jurassic samples indicate a source area domi-nated by Early and Middle Jurassic rocks and containing dominantly Paleozoic, Neoprotero-

zoic, and Mesoproterozoic zircons with subor-dinate late Paleoproterozoic and late Archean zircons (Figs. 8–11). Thus, any potential source area must contain abundant Early and Middle Jurassic igneous rocks. Middle Jurassic zircon ages do not provide a meaningful constraint on source areas for deposits of the Blue Moun-tains Province because appropriate age vol canic and plutonic rocks are ubiquitous along the Cordilleran arc (e.g., Wright and Fahan, 1988; Saleeby and Busby-Spera, 1992; Nokleberg et al., 1994; Busby et al., 2002, 2005; Schermer et al., 2002; Irwin, 2003; Barth et al., 2004; Day and Bickford, 2004; Unruh et al., 2008; many others). Early Jurassic igneous rocks are, how-ever, less widespread in the Cordillera. North of the Blue Mountains, Early Jurassic igne-ous rocks in southern British Columbia (e.g., Mortimer , 1987; Mortimer et al., 1990; Parrish and Monger , 1992; Acton et al., 2001; Fried-man et al., 2002; Schiarizza et al., 2002; Petersen et al., 2004) are not a possible source because Precambrian crystalline rocks and known detrital zircon suites from the region are dominated by ca. 2.0–1.7 and 2.8–2.5 Ga ages (Gehrels and Ross, 1998; Ross et al., 1997). Likewise, po-tential plutonic and sedimentary sources at the present latitude of the Blue Mountains (i.e., Belt Basin and Wyoming craton) are dominated by Paleoproterozoic and Archean zircon (Hoffman, 1989; Gehrels and Ross, 1988; Ross et al., 1997; Ross and Villenvue, 2003) and are a poor match for Jurassic rocks of the Blue Mountains.

More likely sources of Early Jurassic zir-con grains and associated Paleozoic and Pre-cambrian ages are (1) the Black Rock terrane of western Nevada (Wyld, 1990, 1996, 2002; Quinn et al., 1997), (2) the continental seg-ment of the Cordilleran arc (e.g., Saleeby and Busby-Spera, 1992; Busby et al., 2002, 2005; Fackler-Adams et al., 1997; Kowallis et al., 2001; Schermer et al., 2002; Barth et al., 2004), and (3) selected terranes of the Sierra Nevada foothills (Day and Bickford, 2004). The pres-ence of Early Jurassic zircon grains and asso-ciated Paleozoic and Precambrian ages support paleogeographic reconstructions in which the Blue Mountains Province is restored some dis-tance to the south and invite comparisons to known potential inboard sources in the south-western United States.

An excellent match for detrital zircon age distributions in Middle to early Late Jurassic rocks of the Blue Mountains Province is found in southwestern U.S.–enriched, Ouachita-Appa lachian–derived sediment of the late Paleo zoic–early Mesozoic transcontinental river system (Fig. 13; e.g., Rahl et al., 2003; Dickinson and Gehrels, 2003, 2008a, 2008b, 2009). Transcontinental sediment accumulated





in the Triassic backarc basin in Nevada and pro-vided the source for widespread Jurassic ergs of the Colorado Plateau. Jurassic erg sand was, in turn, supplied to the northward-deepening Cor dilleran arc system (Busby-Spera, 1988; Saleeby and Busby-Spera, 1992; Riggs et al., 1996; Manuzak et al., 2000; Busby et al., 2002, 2005; Schermer et al., 2002; Dickinson and Gehrels, 2003, 2008a, 2009; Barth et al., 2004; Leggett et al., 2004).

Robust data sets for detrital zircon ages of transcontinental sand are available for Trias-sic fluvial sandstones of the Colorado Plateau, which were ultimately deposited in the backarc basin of Nevada (recycled backarc-basin source; Dickinson and Gehrels, 2008a), and for Jurassic erg deposits of the southwest Cordillera (Dick-inson and Gehrels, 2003, 2009). These data pro-vide a compelling comparison to coeval Jurassic deposits of the Blue Mountains Province (Fig. 13). Each of these data sets includes notable probability peaks in the range of ca. 485–295 Ma

(Appalachian Paleozoic intrusions) and at ca. 635–615 Ma (peri-Gondwanan terranes and pre-Iapetan rift belts). Grenville age peaks at ca. 1.15 and 1.04 Ga in Blue Mountains samples are strikingly similar to grains in the age range of ca. 1.15 and 1.03 Ga in Triassic backarc basin sands and with age peaks from Jurassic erg samples at ca. 1.16 and 1.05 Ga. We note that Grenville-age detrital zircon signatures from Mexican and Gondwanan sources farther to the south include a distinctly younger age peak (ca. 994–981 Ma; Gillis et al., 2005, and sources therein; Eriks-son et al., 2003; Tassinari et al., 2000), likely precluding derivation of Blue Mountains Prov-ince sands from those regions. Finally, Blue Mountains, recycled backarc basin, Jurassic erg, and Cordilleran arc sands all contain notable enrichments in ca. 1.45–1.3 Ga intracratonic granite ages (also called “anorogenic” granites; cf. Ander son, 1983; Whitmeyer and Karlstrom, 2007) and ca. 1.8–1.6 Ga, southwestern U.S. (Yavapai-Mazatzal)–derived zircons (Fig. 13).

Thus, we conclude that the age distribution of detrital zircon grains in Jurassic samples of the Blue Mountains Province reflects an Ouachita-Appalachian provenance enriched by southwest-ern U.S. and active early Mesozoic Cordilleran arc sources (cf. Dickinson and Gehrels, 2003, 2008a, 2009; Kimbrough et al., 2006).

Implications of Jurassic Detrital Zircon Sources

We consider two likely scenarios by which Early to Middle Jurassic detrital zircon grains and transcontinental sand were delivered to Ju-rassic basins of the Blue Mountains Province: (1) erosion of Jurassic orogenic highlands in western and central Nevada that contained sand originally deposited in an older, Triassic backarc basin (Fig. 13; recycled backarc-basin source), or (2) transport of reworked Jurassic erg sands along a northwestward-flowing arc-parallel, axial river system along the northwestward-deepening Cordilleran arc (Fig. 13; Jurassic

150 160 170 180 190 200 210 220 230 240 250 150 160 170 180 190 200 210 220 230 240 250

195 Keller Creek Shalen =103

180

187 Hyde Fm.n = 88

198Weatherby Fm., Jet Creek mbr.n = 47

198

178

Weatherby Fm., Lower Flyschn = 47

178

196

Weatherby Fm.,Upper Flysch

n = 116

178

195190 Snowshoe Fm.

n = 81

182

Lonesome Fm.n = 132

150

160

170

180

190

John Day Region:Grains <250 Ma

Eastern Oregon:~All ages

Ear

ly J

ura

ssic

Mid

dle

Ju

rass

icL

ate

Jura

ssic

~ D

epo

siti

on

al a

ge

(Ma)

Detrital zircon age (Ma) Detrital zircon age (Ma)

Relative p

rob

ability

168

168

225

220

Jurassic TriassicL M E L M E

Jurassic TriassicL M E L M E

175

194 208

Figure 11. Relative probability plots for Mesozoic samples from the John Day and Huntington, Oregon, areas. Samples are plotted with detrital zircon ages for a given sample location (John Day region vs. Eastern Oregon area) on the x-axis and approximate depositional age on the y-axis. Vertical ruled lines are major divisions of the early Mesozoic time scale.



LaMaskin et al.


erg–type source and Cordilleran arc–type source). It is also possible that both sediment-dispersal pathways were active in Middle to early Late Jurassic time.

Detrital zircon age distributions representing both scenarios are strikingly similar to samples from the Blue Mountains Province (Fig. 13). Close comparison of these data sets, however, suggests that sandstones in the Blue Mountains Province most closely resemble recycled back-arc basin sands. Both suites include a distinctive age peak at ca. 550 Ma, contain a relatively high abundance of ca. 900–700 Ma grains, and lack significant enrichment in Archean grains. Thus, we favor the interpretation that Jurassic sand in the Blue Mountains Province was derived from eroding orogenic highlands in western Nevada (i.e., reworking of deposits from the former backarc basin). This conclusion is speculative because of the relatively small data set for Blue Mountains Province samples. Note that Dick-inson and Gehrels (2008b) interpreted detrital zircon age-distributions in the Upper Jurassic

Morisson Formation to represent recycling from Jurassic erg deposits that were uplifted during the nascent, Middle to Late Jurassic stages of Sevier thrust-belt deformation. Additional de-trital zircon dating of samples from the Blue Mountains, from interstratified quartzose sands of the Cordilleran arc, and from backarc basin deposits in Nevada, is needed to further test and refine our preferred interpretation. Regardless of which sediment-dispersal pattern was domi-nant during early Mesozoic time, the new data presented here indicate that far-traveled, trans-continental sediment was delivered to marginal basins of the Blue Mountains and that these ba-sins were proximal to the craton margin during deposition (i.e., Wyld and Wright, 2001; Dorsey and LaMaskin, 2007; LaMaskin et al., 2008a).

Olds Ferry–Black Rock LinkWyld and Wright (2001) proposed that the

Black Rock terrane of western Nevada and the Olds Ferry terrane of eastern Oregon are dismembered fragments of the same arc. This

model predicts that Late Triassic through Middle Jurassic sedimentary rocks of the Blue Moun-tains were derived from volcanic centers in the Black Rock arc, a prediction that is supported by similarities in deformation history and prov-enance geochemistry between these regions (Wyld et al., 1996; LaMaskin et al., 2008a). If sediments of the upper Aldrich Mountains Group (Keller Creek Shale) were derived from the Olds Ferry–Black Rock arc, this would require initiation of uplift and erosion of the Luning-Fencemaker fold-and-thrust belt (for-mer backarc basin) no later than ca. 181 Ma (LaMaskin , 2009; maximum depositional age of Keller Creek Shale). This is in agreement with constraints on the timing of initial deformation in the Luning-Fencemaker fold-and-thrust belt (ca. 190 Ma; Wyld, 2002; Wyld et al., 2003), the Black Rock arc in the Jackson Mountains and the Pine Forest Range (ca. 201–185; Wyld et al., 1996; Wyld et al., 2003, and references therein), and Late Triassic–Early Jurassic deformation in central Oregon (ca. 215–190; Dickinson and Thayer, 1978). The presence of abundant Early Jurassic detrital zircon grains in Jurassic turbi-dites of the Blue Mountains Province, and ap-parent similarities between Blue Mountains Province sands and recycled backarc basin sands provide additional support for a direct linkage between the Olds Ferry and Black Rock arcs.

Implications for Recycling of Detrital Zircon Grains

Our analysis shows that the detrital zircon age distribution in a sandstone sample may reflect a wide variety of tectonic and sedimentary re-cycling scenarios. Recycling of zircon grains is likely to be the rule rather than the exception, suggesting that caution must be exercised when interpreting detrital zircon U-Pb age data. In particular, the presence of abundant Precam-brian detrital zircon grains in sediment derived from an offshore accretionary subduction com-plex highlights the importance of sediment re-working in detrital zircon studies (cf. Dickinson and Gehrels, 2008b); the presence of Precam-brian detrital zircon grains does not necessarily mean that deposition occurred in proximity to a continental margin. In addition, progressive homogenization of detrital age suites as a result of sedimentary and tectonic recycling means that different potential sediment source areas may possess only slight differences in detrital age spectra (e.g., recycled backarc basin versus Jurassic erg/Cordilleran–arc source; Fig. 13). We therefore suggest that in certain scenarios, a large number of single-grain analyses per sam-ple (i.e., >>100) may be needed to adequately evaluate the presence or absence of diagnostic ages and draw conclusive results.

Fields Creek Fm. ages > 381 Man = 90; This study

0 500 1000 1500 2000 2500 3000

Rel

ativ

e p

rob

abili

ty

Age (Ma)

Yreka terrane, Klamath MountainsSchist of Skookum Gulch, Duzel Phyllite,Sissel Gulch Graywacke, Moffat Creek and Gazelle fms.n = 598; Grove et al. (2008)

Figure 12. Comparison of detrital zircon age distributions among samples from the Yreka terrane, Klamath Mountains, and the Fields Creek Formation. Note large difference in sample size. Only ages older than 381 Ma are plotted (youngest grains in Yreka terrane). Note, ca. 420 Ma and 1.0–2.0 Ga ages occur in both distributions. Yreka samples contain an abundance of ca. 1.5 Ga ages not seen in Fields Creek Formation sample.





0 400 800 1200 1600 2000 2400 2800 3200

Rel

ativ

e p

rob

abili

ty

Age (Ma)

1040

1093

1150

1430

1640 18

50

635

1750

290

All plots include only ages > 285 Ma

615

1055

1160

1465

1675

1855

420

63055

255

1

444

1030

–11

50

1428

1640

–17

06

311

410 10

95 1420

1737

2760

App

alac

hian

Pal

eozo

icIn

trus

ions

Pre

-Iap

etan

Rift

Bel

t and

Per

i-G

ondw

anan

terr

anes

Gre

ater

Gre

nvill

e

Intr

acra

toni

cpl

uton

s

Yav

apai

-M

azat

zal

Laur

entia

ncr

aton

ic

nucl

eus

Inferred Dominant Sources of Grains

Blue Mtns. Mid-Late Jurassicn = 163; This study

Western Nevada, Recycled Back-Arc Basin–Type Sourcen = 1012; Manuzak et al. (2000);Darby et al. (2000); Dickinson and Gehrels (2008a)

Jurassic erg–Type Sourcen = 890; Dickinson and Gehrels (2009)

Cordilleran arc–Type Sourcen = 118; Barth et al. (2004); Dickinsonand Gehrels (2009)

414–475

356–380

Figure 13. Comparison of detrital zircon age distributions in Middle to early Late Jurassic samples from the Blue Mountains (Snowshoe and Lonesome formations) and potential source areas representing recycled backarc-basin transcontinental sand from western Nevada, transcontinental sand from the Jurassic ergs of the Colorado Plateau, and interstratified quartzose sands of Cordilleran arc. For clarity, only ages older than 285 Ma are plotted (cf. Dickinson and Gehrels, 2009). Inferred dominant sources of grains have been modified from Dickinson and Gehrels (2003, 2009) and Whitmeyer and Karlstrom (2007). Data for western Nevada, recycled backarc-basin–type rocks, are published data from Triassic and older assemblages of western Nevada (Luning and Lovelock assemblages—Manuzak et al., 2000; Pass Creek unit and Bishop Canyon Formation—Darby et al., 2000), and from sediment known to have been delivered to the backarc basin during Late Triassic time (Dickinson and Gehrels, 2008, data from their fig. 13). Data for Jurassic Erg–type source are from Dickinson and Gehrels (2009, data from their fig. 7). Data for Cordilleran arc–type source are from Barth et al. (2004; McCoy Mountains Formation, Jurassic samples MC7 and MC9 only) and from Dickinson and Gehrels (2009; Mount Wrightson Formation, sample CP2).



LaMaskin et al.


Sediment-Dispersal and Tectonic Models

Prevailing models for the western U.S. Cor-dillera suggest that the early Mesozoic arc sys-tem was partitioned into a southern continental arc and a northern oceanic arc, with the transi-tion located approximately at the latitude of the Northern Sierra Nevada (Sharp, 1988; Wright and Fahan, 1988; Oldow et al., 1989; Burchfiel et al., 1992; Cowan and Bruhn, 1992; Wyld and Wright, 2001; Gray and Oldow, 2005). Mud-rock geochemistry (LaMaskin et al., 2008a) together with the detrital zircon data presented here support previous suggestions that the Olds Ferry–Black Rock arc is a northward continu-ation of continent-fringing arc systems of the northernmost Sierra Nevada and Klamath Mountains terranes. Next, we propose two ana-logs for the early Mesozoic western U.S. Cor-dillera: the Kamchatka-Kuril and Molucca Sea regions for Middle and Late Triassic time (Fig. 14), and Papua New Guinea region for Jurassic time (Fig. 15).

Middle to Late TriassicThe Kamchatka-Kuril arc region of the

northwest Pacific provides a useful modern analog for the Middle Triassic tectonic setting of the southwestern United States (Figs. 14A and 14B). Both regions are (were) character-ized by a continent-fringing volcanic arc built on inherited basement of accreted terranes, with continental lithosphere that passes along strike to an active offshore arc located outboard of an extensional backarc basin (Figs. 14A and 14B; Geist et al., 1994; Bindeman et al., 2002; Schellart et al., 2003; and references therein). Although the location of the Wallowa terrane during this time interval is uncertain, mudrock geochemistry and detrital zircon geochronology suggest that it was an offshore, intra-oceanic arc (LaMaskin et al., 2008a, 2008b).

Dorsey and LaMaskin (2007, 2008) suggested that the Blue Mountains region underwent a Molucca Sea–type arc-arc collision during Late Triassic time (Figs. 14C and 14D). Detrital zir-con and petrographic data presented here support this model. The large volume of conglomeratic, chert-rich detritus preserved in synorogenic Late Triassic basins requires derivation from a rap-idly eroding, topographically elevated, active thrust-belt source in the Baker terrane accre-tionary subduction complex. The combined data sets support a model for a complex Late Trias-sic collision zone between facing accretionary wedges of (1) the intra-oceanic Wallowa arc and (2) either the Olds Ferry–Black Rock arc or per-haps other arc-related crustal blocks within the Baker terrane (Fig. 14C; LaMaskin et al., 2008a; cf. Schwartz et al., 2010). Figure 14C illus trates

the advance of a growing Baker terrane fold-and-thrust belt into the adjacent Olds Ferry–Black Rock forearc, associated reversal of thrust ver-gence, and Molucca Sea–style consumption of the intervening plate.

It is not clear at present how this Late Trias-sic–Early Jurassic (?) collision zone relates to known structures and more intensely deformed rocks to the south in the Klamath Mountains and Sierra Nevada. We do note, however, that Dick-inson and Lawton (2001) and Dickinson (2006, 2008) suggested a similar double-subduction setting for southward-propagating, diach ronous consumption of the Mezcalera plate beneath portions of the Klamath Mountains and Sierra Nevada, apparently from Early through Middle Jurassic time. It is possible that Late Trias-sic–Early Jurassic (?) deformation in the Blue Mountains Province represents an early phase in this long-lived period of plate consumption. Potential correlation of the outboard Wallowa terrane with outboard terranes of the Klamath Mountains and Sierra Nevada is problematic and beyond the scope of this paper. We pro-pose, however, that rocks and structures in Blue Mountains province may provide insights into the history of the more intensely deformed Klamath-Sierran tectonostratigraphic belts dur-ing Late Triassic time (cf. Dickinson, 2008; Ernst et al., 2008).

Middle JurassicThe tectonic setting of the western U.S.

Cordilleran margin underwent a fundamental change in late Early to Middle Jurassic time (e.g., Wyld, 2002; Wyld et al., 2003). Based on previous stratigraphic synthesis (Dorsey and LaMaskin, 2007, 2008) and new petrographic and detrital zircon data presented here, we sug-gest that the Middle Jurassic Cordilleran mar-gin could have resembled the late Cenozoic

oblique collision of amalgamated arc terranes with the northern margin of Australia in Papua New Guinea (Figs. 15A and 15B; Cooper and Taylor, 1987; Pigram and Davies, 1987; Cloos et al., 2005). Despite some notable differences between the Papuan margin and the Jurassic western United States, both regions have amal-gamated arc terranes that are (were) buttressed against a continental margin in a collisional set-ting, resulting in construction of a large orogenic thrust belt flanked by synorogenic sedimentary basins (Figs. 15A and 15B).

We suggest that Middle–Late Jurassic intra-arc extension in the Klamath Mountains (i.e., Rouge-Chetco arc and Josephine ophiolite) changed along strike to compressional deforma-tion in the Blue Mountains and western Nevada. Rouge-Chetco subduction along the western margin of the Klamath belts may have permit-ted plate convergence to continue following closure of the former backarc region to the east and north (cf. Backarc Geodynamics in Dickin-son, 2006). Modern settings such as Papua New Guinea display large variability in tectonic style along strike of the active plate margin (Fig. 15B; Cloos et al., 2005). Thus, seemingly disparate tectonic histories in Oregon, Nevada, and Cali-fornia may be manifestations of complex micro-plate interactions that are characteristic of an evolving convergent collisional margin.

We also note strikingly similar detrital zircon age distributions in Jurassic turbidites of numer-ous Cordilleran terranes, including the Mari-posa Formation (Sierra Nevada Foothills), rocks of the North Fork terrane (Klamath Mountains), the basal Great Valley Group (California Coast Ranges), the Galice Formation (Klamath Moun-tains), and metagraywackes of the Western Cas-cades (Washington State) (Surpless et al., 2006; MacDonald, 2006; Izsak et al., 2007; Snow and Ernst, 2008; Scherer and Ernst, 2008). These

Figure 14 (on following page). Proposed tectonic models for central western North Amer-ica during Middle and Late Triassic time. Palinspastic base in A and C is modified from Wyld et al. (2006). Rocks of the Blue Mountain Province have been restored ~400 km to the south. OF—Olds Ferry; BR—Black Rock; KM—Klamath Mountains; SN—Sierra Nevada; CA—Cordilleran arc; NAM—North American; H—Huntington; IZ—Izee; WA—Wallowa; BT—Baker terrane. (A) Middle Triassic time. (B) Proposed modern analog of the Kamchatka-Kuril arc region modified from Schellart et al. (2003). Note north arrow. The Kuril backarc basin has rifted from the accreted lithosphere of the Okhotsk microplate. (C) Late Triassic time. Sediment deposited in the John Day region is derived from the out-board Baker terrane accretionary subduction complex. Sediment deposited in the backarc basin is derived from rivers draining the southwestern United States and the Appalachian chain far to the east (i.e., Riggs et al., 1993; Dickinson and Gehrels, 2008). (D) Proposed modern analog of the Molucca Sea region modified from Macpherson and Hall (1999, 2002). The Molucca Sea plate is being subducted to the east and west beneath the Halmahera (HA) and Sangihe (SA) arcs, which form the margins of an orthogonal arc-arc collision. Modern analog does not apply for regions to the south of the Molucca Sea collision.





60°N160°E

Modern Analog:Kamchatka-Kuril Region

Accreted Crust of the Okhotsk

microplateand Kamchatka

peninsula

Activevolcanic

arc

50°N

140°E

150°E

50°N40°N

60°N

140°E

Kamchatka peninsula

N

KurilBackarc

basin

150°E

160°E

40°N Subduction -Accretion Complexes

NV UT

AZ

ORNV

SN

KM

Backarc-basin

WA

?

OF/BR

NAMCraton

CA

H

IZ

Speculative Tectonic Model:Late Triassic

?

Klamath-SierranAccretionary-Subduction Complexes

?Baker-te

rrane

derived sediment

IDNV

sediment

Appalachian sediment

112°W

36°N

40°N

44°N

36°N

40°N

44°N

N

116°W

0 km 200

Miogeocline and

Pz-Mz allocthons

and SW US

Appalachian

UT

C D

NV UT

AZ

ORNV

SN

KM

WA

?

OF/BR

NAMCraton

CA

H

IZ

Speculative Tectonic Model:Middle Triassic

Klamath-SierranAccretionary-Subduction Complexes

IDNV

sediment

Appalachian sediment

112°W

36°N

40°N

44°N

36°N

40°N

44°N

N

116°W

0 km 200

Miogeocline and

Pz-Mz allocthons

and SW US

Appalachian

UT

A B

Modern Analog: Molucca Sea Region

Backarc-basin

BT

Baker

Terrane:Pz-Mz Arcs?

OceanicPlateaus?

N. Sulawesi Trench

N WE

120°E

130°E

0o

10°N

0o

OuterBanda Arc

Sulawesi

Borneo

CelebesSea

Mo

lucca

Sea

HA SA

PhilippineTrench

ContinentalShelf

?

Inner Banda ArcTimor

Fringing arc

Continental arc

Sediment transport directionThrust fault orsubduction zone

Plate margin beneathfold-thrust belt

Subduction zone,uncertain location

EXPLANATION

Spreading centerIntra-oceanic arc

Accretionary complexesof eastern AsiaModern continental shelfof southeastern Asia

Active Kamchatka-Kurilvolcanic arc

Palinspastically restoredstate boundaries

Backarc basin

Figure 14.



LaMaskin et al.


similarities suggest that during Jurassic time (1) transcontinental and recycled sediment-dispersal pathways were widespread, (2) trans-continental sediment was commonly delivered to the Cordilleran arc and forearc region, (3) active orogenic structures and the Mesozoic arc itself were not significant barriers to sediment disper-sal from the craton to the forearc region, and therefore (4) many Jurassic basins of the Cor-dillera were pericratonic and are not far traveled (i.e., >1000 km) with respect to southwestern North America.

SUMMARY AND CONCLUSIONS

Detrital zircon data from central and eastern Oregon confirm the presence of composition-ally distinct sediment source areas that changed from Late Triassic to Late Jurassic time. Upper Triassic sediments were derived from the ad-jacent, outboard Baker terrane and contain two suites of detrital zircon ages: (1) Archean,

Paleo proterozoic, Devonian–Mississippian, and Pennsylvanian ages in the Vester Formation, and (2) dominantly Mesoproterozoic, Silurian–Devo nian, and Permian zircons in the Fields Creek Formation. Similarities in detrital zircon age distributions suggest a genetic link between the Baker terrane source and rocks of the East-ern Klamath and the Northern Sierra terranes, either as an analogous crustal block or via sedi-ment transport and recycling.

Jurassic sandstones contain abundant Meso-protero zoic, Neoproterozoic, Paleozoic, and Early to Middle Jurassic detrital zircon grains. In the John Day region, detrital zircon age dis-tributions in Jurassic sediments closely resemble those of transcontinental sand that was delivered to the western U.S. Cordillera during Triassic and Jurassic time. We infer that sediment was de-livered to Jurassic basins of the Blue Mountains Province by transport of transcontinental sand via either (1) a river system that flowed north along the axis of the Cordilleran arc, or (2) by

erosion and recycling of Triassic backarc basin deposits from collisional orogenic highlands in western and central Nevada (Luning-Fence-maker fold-and-thrust system). Our data support the latter hypothesis, but both are plausible.

Two end members of detrital zircon age dis-tributions recognized elsewhere in Cordilleran basins are represented in the Blue Mountains Province in (1) Triassic samples with abun-dant Archean, Paleoproterozoic, and Paleozoic zircons (i.e., “northwestern Laurentian”), and (2) Jurassic samples enriched in Paleoprotero-zoic, Mesoproterozoic, and Neoproterozoic zir-cons, as well as, Paleozoic and approximately syndepositional Jurassic zircons (i.e., “eastern-southwestern Laurentian”). We suggest that here, and in other early Mesozoic Cordilleran basins, the strong northwestern Laurentian signature may have been recycled from mo-bile, tectonically translated crustal fragments of subduction-accretionary origin, whereas the eastern-southwestern Laurentian transcontinental

SN

KM

OF/BR

CA

H

IZ

BTID

NV

36°N

40°N

44°N

36°N

40°N

44°N

N 0 km 200

Rouge-Chetco Arc

NV UTAZArc-Flank

Dune Sands

Jurassic Eolianites

Luning-FencemakerThrust Belt

Western Jurassic Arc

JO

Utah-

Idah

o Tr

ough

A

CR

O

WA

116°W 112°W

Speculative Tectonic Model:Middle to early Late Jurassic

?

?

Australian Plate

NW

E

Bismark Sea

ManusTrench

New GuineaTrench

CentralRange ForelandIr

ian

-Pap

uan

FT

B

Acc

rete

d a

rcs

B

Woodlark Rise

Modern Analog: Papua New Guinea Region

0 5°S 10°S 15°S

5°N

10°N

135°E

140°E

145°E

150°E

Figure 15. Proposed tectonic models for central western North America during Middle to early Late Jurassic time. See Figure 14 for expla-nation of symbols and abbreviations used. Palinspastic base in A is modified from Wyld et al. (2006). Rocks of the Blue Mountain Province have been restored ~400 km to the south. (A) Middle to early Late Jurassic time. Sediment deposited in the John Day region is derived from (1) tectonic closure, uplift, and erosion of the Triassic backarc basin and formation of the Luning-Fencemaker fold-and-thrust belt, and/or (2) mixed arc and erg dune sands. Similar sediment is deposited in the intra-arc Josephine–Galice (JO) and Coast Range–Basal Great Valley basins (CRO). (B) Proposed modern analog of the Papua New Guinea region modified from Cloos et al. (2005). Note north arrow and flipped E-W arrows. Accretion of the Melanesian arcs has resulted in formation of the Irian-Papuan fold-and-thrust belt (FTB) and deposition in the Central Range foreland. Concomitant transtension is occurring in the Bismark Sea region.





sand signatures may represent an in situ cratonal-recycled provenance.

We propose that the Kamchatka-Kuril and Molucca Sea regions are modern analogs for the western U.S. Cordillera during Middle and Late Triassic time, respectively, and that terrane-continent collision in the Papua New Guinea region is a modern analog for the western U.S. Cor dillera in Jurassic time. Apparent differences between the tectonic setting of accreted ter-ranes in Oregon, Nevada, and California during Middle and Late Jurassic time may be typical aspects of an evolving convergent margin.

ACKNOWLEDGMENTS

This study was supported by funds from the Na-tional Science Foundation to Dorsey (EAR-0537691) and Vervoort (EAR-0537913), and grants from the Geological Society of America, the American Asso-ciation of Petroleum Geologists, SEPM, Sigma Xi, and the University of Oregon to LaMaskin. We thank Daniel Norfleet, Todd Sieber, Leland O’Driscoll, and Andy Lutz for assistance in the field, Charles Knaack and Garret Hart for support with U-Pb laser abla-tion–inductively coupled plasma–mass spectrometry (LA-ICP-MS) analyses, and Diane Wilford and John Donovan for assistance with sample preparation. Paul Wallace generously provided materials and space for sample preparation, and Bill Dickinson miraculously supplied his original thin sections from the John Day region. Marty Grove supplied data from the Yreka area. Discussions with Bill Dickinson, Arthur Snoke, Mark Ferns, Leland O’Driscoll, John Oldow, Tom Peryam, and Sandra Wyld are all appreciated. We specifically extend our gratitude to Ken Ludwig and George Gehrels for making their data analysis and plotting programs freely available and for providing user support. An earlier version of the manuscript bene fited from reviews by Tracy Vallier, Ilya Binde-man, and Greg Retallack. GSA Bulletin reviewers Joshua Schwartz, Gary Ernst, and an anonymous re-viewer provided comments that greatly improved the paper. We thank GSA Bulletin Editor Nancy Riggs and Associate Editor Quentin Crowley for their assistance and comments.

REFERENCES CITED

Acton, S.L., Paradi, S., Thompson, R.I., and Johnston, S.T., 2001, Geological Setting of Paleozoic Strata in the Mount Todd–Adams Lake Region, South-Central British Columbia: Geological Survey of Canada Paper 2001–A7, 14 p.

Alexander, R.S., and Schwartz, J.J., 2009, Detrital zircon geochronology of Permian-Triassic metasedimentary rocks in the Baker terrane, Blue Mountains Province, NE Oregon [abs.]: Geological Society of America Ab-stracts with Programs, v. 41, no. 7, p. 294.

Anderson, J.L., 1983, Proterozoic anorogenic granite plu-tonism of North America, in Medaris, L.G., Jr., Byers, C.W., and Shanks, W.C., eds., Proterozoic Geol-ogy: Geological Society of America Memoir 181, p. 133–154.

Armstrong, R.L., Taubeneck, W.H., and Hales, P.O., 1977, Rb-Sr and K-Ar geochronometry of Mesozoic gra-nitic rocks and their Sr isotopic composition, Ore-gon, Washington, and Idaho: Geological Society of America Bulletin, v. 88, p. 397–411, doi: 10.1130/ 0016-7606(1977)88<397:RAKGOM>2.0.CO;2.

Ashley, R.P., 1995, Petrology and deformation history of the Burnt River Schist and associated plutonic rocks in

the Burnt River Canyon area, northeastern Oregon, in Vallier, T.L., and Brooks, H.C., eds., Geology of the Blue Mountains Region of Oregon, Idaho, and Washington: Petrology and Tectonic Evolution of Pre-Tertiary Rocks of the Blue Mountains Region: U.S. Geological Survey Professional Paper 1438, p. 457–496.

Avé Lallemant, H.G., 1983, The kinematic insignificance of mineral lineations in a Late Jurassic thrust and fold belt in eastern Oregon: Tectonophysics, v. 100, p. 389–404, doi: 10.1016/0040-1951(83)90195-6.

Avé Lallemant, H.G., 1995, Pre-Cretaceous tectonic evo-lution of the Blue Mountains Province, northeastern Oregon, in Vallier, T.L., and Brooks, H.C., eds., Geol-ogy of the Blue Mountains Region of Oregon, Idaho, and Washington: Petrology and Tectonic Evolution of Pre-Tertiary Rocks of the Blue Mountains Region: U.S. Geological Survey Professional Paper 1438, p. 271–304.

Avé Lallemant, H.G., and Oldow, J.S., 1988, Early Meso-zoic southward migration of Cordilleran transpres-sional terranes: Tectonics, v. 7, p. 1057–1075, doi: 10.1029/TC007i005p01057.

Avé Lallemant, H.G., Phelps, D.W., and Sutter, J.F., 1980, 40Ar/39Ar ages of some pre-Tertiary plutonic and metamorphic rocks of eastern Oregon and their geo-logic relationships: Geology, v. 8, p. 371–374, doi: 10.1130/0091-7613(1980)8<371:AAOSPP>2.0.CO;2.

Barth, A.P., Wooden, J.L., Jacobson, C.E., and Probst, K., 2004, U-Pb geochronology and geochemistry of the McCoy Mountains Formation, southeastern Califor-nia: A Cretaceous retroarc foreland basin: Geological Society of America Bulletin, v. 116, p. 142–153, doi: 10.1130/B25288.1; 10.

Bindeman, I.N., Vinogradov, V.I., Valley, J.W., Wooden, J.L., and Natal’in, B.A., 2002, Archean protolith and accretion of crust in Kamchatka: SHRIMP dating of zircons from Sredinny and Ganal Massifs: The Journal of Geology, v. 110, p. 271–289, doi: 10.1086/339532.

Bishop, E.M., 1995a, High-pressure, low-temperature schistose rocks of the Baker terrane, northeastern Ore-gon, in Vallier, T.L., and Brooks, H.C., eds., Geology of the Blue Mountains Region of Oregon, Idaho, and Wash-ington: Petrology and Tectonic Evolution of Pre-Tertiary Rocks of the Blue Mountains Region: U.S. Geological Survey Professional Paper 1438, p. 211–220.

Bishop, E.M., 1995b, Mafic and ultramafic rocks of the Baker terrane, eastern Oregon, and their implications for terrane origin, in Vallier, T.L., and Brooks, H.C., eds., Geology of the Blue Mountains Region of Ore-gon, Idaho, and Washington: Petrology and Tectonic Evolution of Pre-Tertiary Rocks of the Blue Mountains Region: U.S. Geological Survey Professional Paper 1438, p. 221–246.

Blome, C.D., and Nestell, M.K., 1991, Evolution of a Permo-Triassic sedimentary mélange, Grindstone terrane, east-central Oregon: Geological Society of America Bulletin, v. 103, p. 1280–1296, doi: 10.1130/0016-7606 (1991)103<1280:EOAPTS>2.3.CO;2.

Blome, C.D., Jones, D.L., Murchey, B.L., and Liniecki, M., 1986, Geologic implications of radiolarian bearing Paleozoic and Mesozoic rocks from the Blue Moun-tains Province, eastern Oregon, in Vallier, T.L., and Brooks, H.C., eds., Geology of the Blue Mountains Region of Oregon, Idaho, and Washington: Geologic Implications of Paleozoic and Mesozoic Paleontology and Biostratigraphy, Blue Mountains Province, Oregon and Idaho: U.S. Geological Survey Professional Paper 1435, p. 79–101.

Brooks, H.C., 1979, Geologic Map of Huntington and Part of Olds Ferry Quadrangles, Oregon: State of Oregon, Oregon Department of Geology and Mineral Indus-tries, Geologic Map Series GMS-13, scale 1:62,500.

Brooks, H.C., and Vallier, T.L., 1978, Mesozoic rocks and tectonic evolution of eastern Oregon and western Idaho, in Howell, D.G., and McDougall, K.A., eds., Mesozoic Paleogeography of the Western United States: Society of Economic Paleontologists and Min-eralogists, Pacific Section, Paleogeography Sympo-sium 2, p. 133–145.

Brooks, H.C., McIntyre, J.R., and Walker, G.W., 1976, Geol ogy of the Oregon Part of the Baker 1-Degree by

2-Degree Quadrangle: State of Oregon, Oregon De-partment of Geology and Mineral Industries, Geologic Map Series GMS-7, scale 1:250,000.

Brown, C.E., and Thayer, T.P., 1966, Geologic Map of the Canyon City Quadrangle, Northeastern Oregon: U.S. Geological Survey Map I-447, scale 1:250,000.

Brown, C.E., and Thayer, T.P., 1977, Geologic Map of Pre-Tertiary Rocks in the Eastern Aldrich Mountains and Adjacent Areas to the South, Grant County, Oregon: U.S. Geological Survey Miscellaneous Investigations Map I-1021, scale 1:62,500.

Brown, E.H., and Gehrels, G.E., 2007, Detrital zircon con-straints on terrane ages and affinities and timing of orogenic events in the San Juan Islands and North Cascades, Washington: Canadian Journal of Earth Sci-ences, v. 44, p. 1375–1396, doi: 10.1139/E07-040.

Burchfiel, B.C., Cowan, D.S., and Davis, G.A., 1992, Tectonic overview of the Cordilleran orogen in the western U.S., in Burchfiel, B.C., Lipman, P.W., and Zoback, M.L., eds., The Cordilleran Orogen: Conter-minous U.S.: Boulder, Colorado, Geological Society of America, The Geology of North America, v. G-3, p. 407–480.

Busby, C.J., Schermer, E.R., and Mattinson, J.M., 2002, Extensional arc setting and ages of Middle Jurassic eolianites, Cowhole Mountains (eastern Mojave Desert block, California), in Glazner, A.F., Walker, J.D., and Bartley, J.M., eds., Geologic Evolution of the Mojave Desert and Southwestern Basin and Range: Geological Society of America Memoir 195, p. 79–91.

Busby, C.J., Bassett, K., Steiner, M.B., and Riggs, N., 2005, Climatic and tectonic controls on Jurassic intra-arc basins related to northward drift of North America, in Anderson, T.H., Nourse, J.A., McKee, J.W., and Steiner, M.B., eds., The Mojave-Sonora Megashear Hypothesis: Development, Assessment, and Alterna-tives: Geological Society of America Special Paper 393, p. 359–376, doi: 10.1130/2005.2393(13).

Busby-Spera, C.J., 1988, Speculative tectonic model for the early Mesozoic arc of the southwest Cordilleran United States: Geology, v. 16, p. 1121–1125, doi: 10.1130/ 0091-7613(1988)016<1121:STMFTE>2.3.CO;2.

Carpenter, P.S., and Walker, N.W., 1992, Origin and tectonic significance of the Aldrich Mountains serpentinite matrix mélange, northeastern Oregon: Tectonics, v. 11, p. 690–708, doi: 10.1029/91TC03013.

Chang, Z., Vervoort, J.D., McClelland, W.C., and Knaack, C., 2006, U-Pb dating of zircon by LA-ICP-MS: Geo-chemistry, Geophysics, Geosystems, v. 7, p. Q05009, doi: 10.1029/2005GC001100.

Cloos, M., Sapiie, B., Quarles van Ufford, A., Weiland, R.J., Warren, P.Q., and McMahon, T.P., 2005, Col-lisional Delamination in New Guinea: The Geo-tectonics of Subducting Slab Breakoff: Geological Society of America Special Paper 400, 51 p., doi: 10.1130/2005.2400.

Cooper, P., and Taylor, B., 1987, Seismotectonics of New Guinea; a model for arc reversal following arc-conti-nent collision: Tectonics, v. 6, p. 53–67, doi: 10.1029/TC006i001p00053.

Cowan, D.S., and Bruhn, R.L., 1992, Late Jurassic to early Late Cretaceous geology of the U.S. Cordillera, in Burchfiel, B.C., Lipman, P.W., and Zoback, M.L., editors, The Cordilleran Orogen: Conterminous U.S.: Boulder, Colorado, Geological Society of America, The Geology of North America, v. G-3, p. 169–203.

Coward, R.I., 1983, Structure, Stratigraphy, and Petrology of the Elkhorn Ridge Argillite, Sumpter Area, Northeast-ern Oregon [Ph.D. dissertation]: Houston, Texas, Rice University, 144 p.

Critelli, S., and Ingersoll, R.V., 1995, Interpretation of neovolcanic versus palaeovolcanic sand grains: An example from Miocene deep-marine sandstone of the Topanga Group (Southern California): Sedimentol-ogy, v. 42, p. 783–804, doi: 10.1111/j.1365-3091.1995 .tb00409.x.

Darby, B.J., Wyld, S.J., and Gehrels, G.E., 2000, Provenance and paleogeography of the Black Rock terrane, north-western Nevada: Implications of U-Pb detrital zircon geochronology, in Soreghan, M.J., and Gehrels, G.E., eds., Paleozoic and Triassic Paleogeography and Tec-tonics of Western Nevada and Northern California:



LaMaskin et al.


Geological Society of America Special Paper 347, p. 77–87, doi: 10.1130/0-8137-2347-7.77.

Day, H.W., and Bickford, M., 2004, Tectonic setting of the Jurassic Smartville and Slate Creek complexes, north-ern Sierra Nevada, California: Geological Society of America Bulletin, v. 116, p. 1515–1528, doi: 10.1130/B25416.1.

DeGraaff-Surpless, K., Mahoney, B., Wooden, J., and McWilliams , M., 2003, Lithofacies control in detrital zircon provenance studies: Insights from the Creta-ceous Methow Basin, southern Canadian Cor dillera: Geological Society of America Bulletin, v. 115, p. 899–915, doi: 10.1130/B25267.1.

Dickinson, W.R., 1970, Interpreting detrital modes of grey-wacke and arkose: Journal of Sedimentary Petrology, v. 40, no. 2, p. 695–707.

Dickinson, W.R., 1979, Mesozoic forearc basin in cen-tral Oregon: Geology, v. 7, no. 4, p. 166–170, doi: 10.1130/0091-7613(1979)7<166:MFBICO>2.0.CO;2.

Dickinson, W.R., 1985, Interpreting provenance relations from detrital modes of sandstones, in Zuffa, G.G., ed., Provenance of Arenites: Dordrecht, Reidel Publishing Company, NATO ASI Series, p. 333–361.

Dickinson, W.R., 2000, Geodynamic interpretation of Paleo-zoic tectonic trends oriented oblique to the Mesozoic Klamath-Sierran continental margin in California, in Soreghan, M.J., and Gehrels, G.E., eds., Paleozoic and Triassic Paleogeography and Tectonics of Western Ne-vada and Northern California: Geological Society of America Special Paper 347, p. 209–245.

Dickinson, W.R., 2004, Evolution of the North Ameri-can Cordillera: Annual Review of Earth and Plan-etary Sciences, v. 32, p. 13–45, doi: 10.1146/annurev .earth.32.101802.120257.

Dickinson, W.R., 2006, Geotectonic evolution of the Great Basin: Geosphere, v. 2, p. 353–368, doi: 10.1130/GES00054.1.

Dickinson, W.R., 2008, Accretionary Mesozoic–Ceno-zoic expansion of the Cordilleran continental margin in California and adjacent Oregon: Geosphere, v. 4, p. 329–353, doi: 10.1130/GES00105.1.

Dickinson, W.R., and Gehrels, G.E., 2000, Sandstone petro-facies of detrital zircon samples from Paleozoic and Triassic strata in suspect terranes of northern Nevada and California, in Soreghan, M.J., and Gehrels, G.E., eds., Paleozoic and Triassic Paleogeography and Tec-tonics of Western Nevada and Northern California: Geological Society of America Special Paper 347, p. 151–171, doi: 10.1130/0-8137-2347-7.151.

Dickinson, W.R., and Gehrels, G.E., 2003, U-Pb ages of detrital zircons from Permian and Jurassic eolian sand-stones of the Colorado Plateau, USA: Paleogeographic implications: Sedimentary Geology, v. 163, p. 29–66, doi: 10.1016/S0037-0738(03)00158-1.

Dickinson, W.R., and Gehrels, G.E., 2008a, U-Pb ages of detrital zircons in relation to paleogeography; Triassic paleodrainage networks and sediment dispersal across southwest Laurentia: Journal of Sedimentary Research, v. 78, p. 745–764, doi: 10.2110/jsr.2008.088.

Dickinson, W.R., and Gehrels, G.E., 2008b, Sediment de-livery to the Cordilleran foreland basin: Insights from U-Pb ages of detrital zircons in Upper Jurassic and Cretaceous strata of the Colorado Plateau: American Journal of Science, v. 308, December, p. 1041–1082, doi: 10.2475/10.2008.01.

Dickinson, W.R., and Gehrels, G.E., 2009, U-Pb ages of detrital zircons in Jurassic eolian and associated sand-stones of the Colorado Plateau: Evidence for trans-continental dispersal and intraregional recycling of sediment: Geological Society of America Bulletin, v. 121, p. 408–433, doi: 10.1130/B26406.1.

Dickinson, W.R., and Lawton, T.F., 2001, Carboniferous to Cretaceous assembly and fragmentation of Mex-ico: Geological Society of America Bulletin, v. 113, p. 1142–1160, doi: 10.1130/0016-7606(2001)113 <1142:CTCAAF>2.0.CO;2.

Dickinson, W.R., and Suczek, C.A., 1979, Plate tectonics and sandstone composition: The American Association of Petroleum Geologists Bulletin, v. 63, p. 2164–2172.

Dickinson, W.R., and Thayer, T.P., 1978, Paleogeographic and paleotectonic implications of Mesozoic stratig-raphy and structure in the John Day Inlier of central

Oregon, in Howell, D.G., and McDougall, K.A., eds., Mesozoic Paleogeography of the Western United States: Society of Economic Paleontologists and Min-eralogists, Pacific Section, Paleogeography Sympo-sium 2, p. 147–161.

Dickinson, W.R., and Vigrass, L.W., 1965, Geology of the Suplee-Izee Area, Crook, Grant, and Harney Counties, Oregon: Oregon Department of Geology and Mineral Industries Bulletin 58, 109 p.

Dickinson, W.R., Helmold, K.P., and Stein, J.A., 1979, Meso zoic lithic sandstones in central Oregon: Journal of Sedimentary Petrology, v. 49, p. 501–516.

Dickinson, W.R., Beard, L.S., Brakenridge, G.R., Erjavec, J.L., Ferguson, R.C., Inman, K.F., Knepp, R.A., Lind-berg, F.A., and Ryberg, P.T., 1983, Provenance of North American Phanerozoic sandstones in relation to tec-tonic setting: Geological Society of America Bulletin, v. 94, p. 222–235, doi: 10.1130/0016-7606(1983)94 <222:PONAPS>2.0.CO;2.

Dickinson, W.R., Hopson, C.A., and Saleeby, J.B., 1996, Alter nate origins of the Coast Range ophiolite (Cali-fornia): Introduction and implications: GSA Today, v. 6, no. 2, p. 1–2.

Dorsey, R.J., and LaMaskin, T.A., 2007, Stratigraphic record of Triassic-Jurassic collisional tectonics in the Blue Mountains Province, northeastern Oregon: Ameri-can Journal of Science, v. 307, p. 1167–1193, doi: 10.2475/10.2007.03.

Dorsey, R.J., and LaMaskin, T.A., 2008, Mesozoic collision and accretion of oceanic terranes in the Blue Moun-tains Province of northeastern Oregon: New insights from the stratigraphic record, in Spencer, J.E., and Titley, S.R., eds., Circum-Pacific Tectonics, Geologic Evolution, and Ore Deposits: Arizona Geological So-ciety Digest, v. 22, p. 325–332.

Eriksson, K.A., Campbell, I.H., Palin, J.M., and Allen, C.M., 2003, Predominance of Grenville magmatism recorded in detrital zircons from modern Appalachian rivers: The Journal of Geology, v. 111, p. 707–717, doi: 10.1086/378338.

Ernst, W.G., Snow, C.A., and Scherer, H.H., 2008, Con-trasting early and late Mesozoic petrotectonic evo-lution of northern California: Geological Society of America Bulletin, v. 120, p. 179–194, doi: 10.1130/B26173.1.

Fackler-Adams, B.N., Busby, C.J., and Mattinson, J.M., 1997, Jurassic magmatism and sedimentation in the Palen Mountains, southeastern California: Implications for regional tectonic controls on the Mesozoic magmatic arc: Geological Society of America Bulletin, v. 109, p. 1464–1484, doi: 10.1130/0016-7606(1997)109 <1464:JMASIT>2.3.CO;2.

Ferns, M.L., and Brooks, H.C., 1995, The Bourne and Greenhorn subterranes of the Baker terrane, north-eastern Oregon: Implications for the evolution of the Blue Mountains island-arc system, in Vallier, T.L., and Brooks, H.C., eds., Geology of the Blue Mountains Re-gion of Oregon, Idaho and Washington: Petrology and Tectonic Evolution of Pre-Tertiary Rocks of the Blue Mountains Region: U.S. Geological Survey, Profes-sional Paper 1438, p. 331–358.

Ferns, M.L., Madin, I.P., and Taubeneck, W.H., 2001, Recon-naissance Geologic Map of the La Grande 30′ × 60′ Quadrangle, Baker, Grant, Umatilla, and Union Coun-ties, Oregon: Oregon Department of Geology and Min-eral Industries Reconnaissance Map Series RMS-1, scale 1:24,000, 52 p.

Friedman, R., Ray, G., and Webster, I., 2002, U-Pb Zircon and titanite dating of intrusive rocks in the Heffley Lake area, south-central British Columbia, in Geologi-cal Fieldwork: British Columbia Ministry of Energy and Mines Paper 2002–1, p. 109–118.

Garzanti, E., Ando, S., and Scutella, M., 2000, Actualistic ophiolite provenance: The Cyprus case: The Journal of Geology, v. 108, p. 199–218, doi: 10.1086/314391.

Garzanti, E., Doglioni, C., Vezzoli, G., and Ando, S., 2007, Orogenic belts and orogenic sediment provenance: The Journal of Geology, v. 115, p. 315–334, doi: 10.1086/512755.

Gehrels, G.E., 2000, Introduction to detrital zircon studies of Paleozoic and Triassic strata in western Nevada and northern California, in Soreghan, M.J., and Gehrels,

G.E., eds., Paleozoic and Triassic Paleogeography and Tectonics of Western Nevada and Northern California: Geological Society of America Special Paper 347, p. 1–17, doi: 10.1130/0-8137-2347-7.1.

Gehrels, G.E., and Kapp, P.A., 1998, Detrital zircon geo-chronology and regional correlation of metasedi-mentary rocks in the Coast Mountains, southeastern Alaska: Canadian Journal of Earth Sciences, v. 35, p. 269–279, doi: 10.1139/cjes-35-3-269.

Gehrels, G.E., and Miller, M.M., 2000, Detrital zircon geo-chronologic study of Upper Paleozoic strata in the east-ern Klamath terrane, northern California, in Soreghan, M.J., and Gehrels, G.E., eds., Paleozoic and Triassic Paleogeography and Tectonics of Western Nevada and Northern California: Geological Society of America Special Paper 347, p. 99–108.

Gehrels, G.E., and Ross, G.M., 1998, Detrital zircon geo-chronology of Neoproterozoic to Permian mio geo-clinal strata in British Columbia and Alberta: Canadian Journal of Earth Sciences, v. 35, p. 1380–1401, doi: 10.1139/cjes-35-12-1380.

Gehrels, G.E., Dickinson, W.R., Ross, G.M., Stewart, J.H., and Howell, D.G., 1995, Detrital zircon reference for Cam-brian to Triassic miogeoclinal strata of western North America: Geology, v. 23, p. 831–834, doi: 10.1130/ 0091-7613(1995)023<0831:DZRFCT>2.3.CO;2.

Gehrels, G.E., Dickinson, W.R., Darby, B.J., Harding, J.P., Manuszak, J.D., Riley, B.C.D., Spurlin, M.S., Finney, S.C., Girty, G.H., Harwood, D.S., Miller, M.M., Satter-field, J.I., Smith, M.T., Snyder, W.S., Wallin, E.T., and Wyld, S.J., 2000, Tectonic implications of detrital zir-con data from Paleozoic and Triassic strata in western Nevada and Northern California, in Soreghan, M.J., and Gehrels, G.E., eds., Paleozoic and Triassic Paleogeog-raphy and Tectonics of Western Nevada and Northern California: Geological Society of America Special Paper 347, p. 133–150, doi: 10.1130/0-8137-2347-7.133.

Gehrels, G.E., Valencia, V., and Pullen, A., 2006, Detrital zircon geochronology by laser-ablation multicollec-tor ICPMS at the Arizona Laser-Chron Center, in Olszewski , T., and Huff, W., eds., Geochronology: Emerging Opportunities: Philadelphia, Pennsylvania, Paleontological Society Short Course, p. 1–10.

Geist, E.L., Vallier, T.L., and Scholl, D.W., 1994, Origin, transport, and emplacement of an exotic island-arc ter-rane exposed in eastern Kamchatka, Russia: Geologi-cal Society of America Bulletin, v. 106, p. 1182–1194, doi: 10.1130/0016-7606(1994)106<1182:OTAEOA>2.3.CO;2.

Getty, S.R., Selverstone, J., Wernicke, B.P., Jacobsen, S.B., Aliberti, E., and Lux, D.R., 1993, Sm-Nd dating of multiple garnet growth events in an arc-continent colli-sion zone, northwestern U.S. Cordillera: Contributions to Mineralogy and Petrology, v. 115, p. 45–57, doi: 10.1007/BF00712977.

Gillis, R.J., Gehrels, G.E., Ruiz, J., and Flores de Dios Gonzalez, L.A., 2005, Detrital zircon provenance of Cambrian-Ordovician and Carboniferous strata of the Oaxaca terrane, southern Mexico: Sedimentary Geology, v. 182, p. 87–100, doi: 10.1016/j.sedgeo .2005.07.013.

Giorgis, S., Tikoff, B., and McClelland, W., 2005, Missing Idaho arc: Transpressional modification of the 87Sr/86Sr transition on the western edge of the Idaho batholith: Geology, v. 33, p. 469–472, doi: 10.1130/G20911.1.

Giorgis, S., McClelland, W., Fayon, A., Singer, B.S., and Tikoff, B., 2008, Timing of deformation and exhuma-tion in the western Idaho shear zone, McCall, Idaho: Geological Society of America Bulletin, v. 120, p. 1119–1133, doi: 10.1130/B26291.1.

Graham, S.A., Hendrix, M.S., Wang, L.B., and Carroll, A.R., 1993, Collisional successor basins of western China: Impact of tectonic inheritance on sand com-position: Geological Society of America Bulletin, v. 105, p. 323–344, doi: 10.1130/0016-7606(1993)105 <0323:CSBOWC>2.3.CO;2.

Gray, K.D., and Oldow, J.S., 2005, Contrasting structural histories of the Salmon River belt and Wallowa ter-rane: Implications for terrane accretion in northeastern Oregon and west-central Idaho: Geological Society of America Bulletin, v. 117, p. 687–706, doi: 10.1130/B25411.1.





Grove, M., Gehrels, G.E., Cotkin, S.J., Wright, J.E., and Zou, H., 2008, Non-Laurentian cratonal provenance of Late Ordovician eastern Klamath blueschists and a link to the Alexander terrane, in Wright, J.E., and Shervais, J.W., eds., Ophiolites, Arcs, and Batholiths: A Tribute to Cliff Hopson: Geological Society of America Special Paper 438, p. 223–250, doi: 10.1130/2008.2438(08).

Hacker, B.R., and Goodge, J.W., 1990, Comparison of early Mesozoic high-pressure rocks in the Klamath Moun-tains and Sierra Nevada, in Harwood, D.S., and Miller, M.M., eds., Paleozoic and Early Mesozoic Paleogeo-graphic Relations: Sierra Nevada, Klamath Mountains, and Related Terranes: Geological Society of America Special Paper 255, p. 277–295.

Hamilton, W.B., 1963, Metamorphism in the Riggins Re-gion, Western Idaho: U.S. Geological Survey Profes-sional Paper 436, 95 p.

Hanson, R.E., Saleeby, J.B., and Schweickert, R.A., 1988, Composite Devonian island-arc batholith in the north-ern Sierra Nevada, California: Geological Society of America Bulletin, v. 100, p. 446–457, doi: 10.1130/ 0016-7606(1988)100<0446:CDIABI>2.3.CO;2.

Harding, J.P., Gehrels, G.E., Harwood, D.S., and Girty, G.H., 2000, Detrital zircon geochronology of the Shoo Fly Complex, northern Sierra terrane, northeastern California, in Soreghan, M.J., and Gehrels, G.E., eds., Paleozoic and Triassic Paleogeography and Tectonics of Western Nevada and Northern California: Geologi-cal Society of America Special Paper 347, p. 43–55, doi: 10.1130/0-8137-2347-7.43.

Harper, G.D., and Wright, J.E., 1984, Middle to Late Ju-rassic tectonic evolution of the Klamath Mountains, California-Oregon: Tectonics, v. 3, p. 759–772, doi: 10.1029/TC003i007p00759.

Hendricksen, T.A., Skurla, S.J., and Field, C.W., 1972, K-Ar dates for plutons from the Iron Mountain and Stur-gill Peak areas of western Idaho: Isochron-West, v. 5, p. 13–16.

Hoffman, P.F., 1989, Precambrian geology and tectonic his-tory of North America, in Bally, A.W., and Palmer, A.R., eds., The Geology of North America—An Over-view: Boulder, Colorado, Geological Society of Amer-ica, v. A, p. 447–512.

Hooper, P.R., Houseman, M.D., Beane, J.E., Caffrey, G.M., Engh, K.R., Scrivner, J.V., and Watkinson, A.J., 1995, Geology of the northern part of the Ironside Moun-tain Inlier, northeastern Oregon, in Vallier, T.L., and Brooks, H.C., eds., Geology of the Blue Mountains Region of Oregon, Idaho, and Washington: Petrology and Tectonic Evolution of Pre-Tertiary Rocks of the Blue Mountains Region: U.S. Geological Survey Pro-fessional Paper 1438, p. 415–456.

Horn, I., Rudnick, R.L., and McDonough, W.F., 2000, Precise elemental and isotope ratio determination by simultaneous solution nebulization and laser abla-tion-ICP-MS: Application to U-Pb geochronology: Chemical Geology, v. 164, p. 281–301, doi: 10.1016/S0009-2541(99)00168-0.

Hotz, P.E., Lanphere, M.A., and Swanson, D.A., 1977, Triassic blueschist from northern California and north-central Oregon: Geology, v. 5, p. 659–663, doi: 10.1130/0091-7613(1977)5<659:TBFNCA>2.0.CO;2.

Housen, B.A., and Dorsey, R.J., 2005, Paleomagnetism and tectonic significance of Albian and Cenomanian tur-bidites, Ochoco basin, Mitchell Inlier, central Oregon: Journal of Geophysical Research, v. 110, p. B07102, doi: 10.1029/2004JB003458.

Imlay, R.W., 1986, Jurassic ammonites and biostratigraphy of eastern Oregon and western Idaho, in Vallier, T.L., and Brooks, H.C., eds., Geology of the Blue Mountains Region of Oregon, Idaho, and Washington: Geologic Implications of Paleozoic and Mesozoic Paleontology and Biostratigraphy, Blue Mountains Province, Oregon and Idaho: U.S. Geological Survey Professional Paper 1435, p. 53–57.

Ingersoll, R.V., and Schweickert, R.A., 1986, A plate-tectonic model for Late Jurassic ophiolite genesis, Nevadan orogeny and forearc initiation, northern California: Tectonics, v. 5, p. 901–912, doi: 10.1029/TC005i006p00901.

Ingersoll, R.V., and Suczek, C.A., 1979, Petrology and prov-enance of Neogene sand from Nicobar and Bengal

fans, DSDP Sites 211 and 218: Journal of Sedimentary Petrology, v. 49, p. 1217–1228.

Ingersoll, R.V., Fullard, T.F., Ford, R.L., Grimm, J.P., Pickle, J.D., and Sares, S.W., 1984, The effect of grain size on detrital modes: A test of the Gazzi-Dickinson point-counting method: Journal of Sedimentary Petrology, v. 54, p. 103.

Irwin, W.P., 2003, Correlation of the Klamath Mountains and Sierra Nevada: U.S. Geological Survey Open-File Report 02–0490, 2 sheets.

Izsak, G., Wright, J.E., Wyld, S., Kimbrough, D., and Grove, M., 2007, Paleogeographic implications of similar detrital zircon signatures in mostly Jurassic and Cre-taceous strata from Idaho to southern Baja California [abs.]: Geological Society of America Abstracts with Programs, v. 39, no. 4, p. 8.

Jones, D.L., Pessagno, E.A., Jr., Force, E.R., and Irwin, W.P., 1976, Jurassic radiolarian chert from near John Day, Oregon: Geological Society of America Abstracts with Programs, v. 8, no. 3, p. 386.

Kays, M.A., Stimac, J.P., and Goebel, P.M., 2006, Permian-Jurassic growth and amalgamation of the Wallowa composite terrane, northeastern Oregon, in Snoke, A.W., and Barnes, C.G., eds., Geological Studies in the Klamath Mountains Province, California and Oregon: Geological Society of America Special Paper 410, p. 465–494.

Kimbrough, D.L., Abbott, P.L., Grove, M., Smith, D.P., Mahoney, J.B., Moore, T.E., and Gehrels, G.E., 2006, Contrasting cratonal provenances for Upper Creta-ceous Valle Group quartzite clasts, Baja California, in Girty, G.H., and Cooper, J.D., eds., Using Stratig-raphy, Sedimentology, and Geochemistry to Unravel the Geologic History of the Southwestern Cordillera: A Volume in Honor of Patrick L. Abbott: Pacific Sec-tion, SEPM 101, book no. 101, p. 97–110.

Kowallis, B.J., Christiansen, E.H., Deino, A.L., Zhang, C., and Everett, B.H., 2001, The record of Middle Jurassic volcanism in the Carmel and Temple Cap Formations of southwestern Utah: Geological Society of America Bulletin, v. 113, p. 373–387, doi: 10.1130/0016-7606 (2001)113<0373:TROMJV>2.0.CO;2.

LaMaskin, T.A., 2008, Late Triassic (Carnian-Norian) mixed volcaniclastic-carbonate facies of the Olds Ferry terrane, eastern Oregon and western Idaho, in Blodgett, R., and Stanley, G., eds., The Terrane Puzzle: New Perspectives on Paleontology and Stratigraphy from the North American Cordillera: Geological Society of America Special Paper 442, p. 251–267.

LaMaskin, T.A., 2009, Stratigraphy, Provenance, and Tec-tonic Evolution of Mesozoic Basins in the Blue Moun-tains Province, Eastern Oregon and Western Idaho [Ph.D. dissertation]: Eugene, Oregon, University of Oregon, 232 p.

LaMaskin, T.A., Dorsey, R.J., and Vervoort, J.V., 2008a, Tectonic controls on mudrock geochemistry, Mesozoic rocks of eastern Oregon and western Idaho, U.S.A.: Implications for Cordilleran tectonics: Journal of Sedi-mentary Research, v. 78, p. 765–783, doi: 10.2110/jsr.2008.087.

LaMaskin, T.A., Vervoort, J., and Dorsey, R.J., 2008b, Geochemical, isotopic and detrital-zircon provenance of Mesozoic rocks, Oregon and Idaho, U.S.A. [abs.]: Goldschmidt 2008, Vancouver, B.C.: Geochimica et Cosmochimica Acta, v. 72, p. A513.

LaMaskin, T.A., Schwartz, J.J., Dorsey, R.J., Snoke, A.W., Johnson, K., and Vervoort, J.D., 2009, Meso-zoic sedimentation, magmatism, and tectonics in the Blue Mountains Province, northeastern Oregon, in O’Connor, J.E., Dorsey, R.J., and Madin, I.P., eds., Volcanoes to Vineyards: Geologic Field Trips through the Dynamic Landscape of the Pacific Northwest: Geo-logical Society of America Field Guide 15, p. 187–202, doi: 10.1130/2009.fld015(09).

Leeman, W.P., Avé Lallemant, H.G., Gerlach, D.C., Sutter, J.F., and Arculus, R.J., 1995, Petrology of the Canyon Mountain complex, in Vallier, T.L., and Brooks, H.C., eds., Geology of the Blue Mountains Region of Ore-gon, Idaho, and Washington: Petrology and Tectonic Evolution of Pre-Tertiary Rocks of the Blue Mountains Region: U.S. Geological Survey Professional Paper 1438, p. 1–43.

Leggett, W., Lawton, T., Amaton, J., Gonzalez-Leon, C., and Gehrels, G., 2004, New detrital zircon data from a quartz arenite northwest of Cucurpe, north-central Sonora , Mexico: Implications for Middle to Late Jurassic basin development along the southwest-ern margin of North America: Geological Society of America Abstracts with Programs, v. 36, no. 5, p. 510.

Lewis, R.S., 2002, Geologic Maps of Nez Perce, Lewis, Idaho, Adams and Washington Counties: Digital Atlas of Idaho: http://imnh.isu.edu/digitalatlas/ (last accessed 1 October, 2008).

Ludwig, K.R., 2003, Isoplot 3.00: Berkeley Geochronology Center Special Publication 4, 70 p.

Lund, K., 2004, Geology of the Payette National Forest and Vicinity, West-Central Idaho: U.S. Geological Survey Professional Paper 1666-A, 1666-B, 89 p.

Lund, K., and Snee, L.W., 1988, Metamorphism, structural development, and age of the continent-island arc junc-ture in west-central Idaho, in Ernst, W.G., ed., Meta-morphism and Crustal Evolution of the Western United States, Rubey Volume III: Englewood Cliffs, New Jer-sey, Prentice Hall, p. 297–331.

Lund, K., Aleinikoff, J.N., Yacob, E.Y., Unruh, D.M., and Fanning, C.M., 2008, Coolwater culmination: Sensi-tive high-resolution ion microprobe (SHRIMP) U-Pb and isotopic evidence for continental delamination in the Syringa Embayment, Salmon River suture, Idaho: Tectonics, v. 27, p. TC2009, doi: 10.1029/ 2006TC002071.

MacDonald, J.H., Jr., 2006, Petrology, Petrogenesis, and Tectonic Setting of Jurassic Rocks of the Central Cas-cades, Washington, and Western Klamath Mountains, California-Oregon [Ph.D. dissertation]: Albany, New York, State University of New York at Albany, 415 p.

Macpherson, C.G., and Hall, R., 1999, Tectonic controls on geochemical evolution in arc magmatism in SE Asia, in Proceedings of the 4th PACRIM Congress: Australian Institute of Mining and Metallurgy, Bali, Indonesia, p. 359–368.

Macpherson, C.G., and Hall, R., 2002, Timing and tectonic controls in the evolving orogen of SE Asia and the western Pacific and some implications for ore genera-tion, in Blundell, D.J., Neubauer, E., and Von Quadt, A., eds., The Timing and Location of Major Ore De-posits in an Evolving Orogen: Geological Society of London Special Publication 204, p. 49–67, doi: 10.1144/GSL.SP.2002.204.01.04.

Manduca, C.A., Silver, L.T., and Taylor, H.P., 1992, 87Sr/86Sr and 19O/16O isotopic systematics and geochemistry of granitoid plutons across a steeply-dipping boundary between contrasting lithospheric blocks in western Idaho: Contributions to Mineralogy and Petrology, v. 109, p. 355–372, doi: 10.1007/BF00283324.

Manduca, C.A., Kuntz, M.A., and Silver, L.T., 1993, Em-placement and deformation history of the western mar-gin of the Idaho batholith near McCall, Idaho: Influence of a major terrane boundary: Geological Society of America Bulletin, v. 105, p. 749–765, doi: 10.1130/ 0016-7606(1993)105<0749:EADHOT>2.3.CO;2.

Mann, G.M., and Vallier, T.L., 2007, Mesozoic telescoping of island arc terranes and geologic evolution of the Cuddy Mountains region, western Idaho, in Kuntz, M.A., and Snee, L.W., eds., Geological Studies of the Salmon River Suture Zone and Adjoining Areas, West-Central Idaho and Eastern Oregon: U.S. Geological Survey Professional Paper 1738, p. 123–162.

Manuzak, J.D., Satterfield, J.I., and Gehrels, G.E., 2000, Detrital-zircon geochronology of Upper Triassic strata in western Nevada, in Soreghan, M.J., and Gehrels, G.E., eds., Paleozoic and Triassic Paleogeography and Tectonics of Western Nevada and Northern California: Geological Society of America Special Paper 347, p. 109–118.

McClelland, W.C., Gehrels, G.E., and Saleeby, J.B., 1992, Upper Jurassic–Lower Cretaceous basinal strata along the Cordilleran margin: Implications for the accretionary history of the Alexander-Wrangellia-Peninsular terrane: Tectonics, v. 11, p. 823–835, doi: 10.1029/92TC00241.

McClelland, W.C., Tikoff, B., and Manduca, C.A., 2000, Two-phase evolution of accretionary margins: Ex-amples from the North American Cordillera : Tectono-



LaMaskin et al.


physics, v. 326, p. 37–55, doi:10.1016S0040-1951 (00)00145-1.

Miller, E.L., Miller, M.M., Stevens, C.H., Wright, J.E., and Madrid, R., 1992, Late Paleozoic paleogeography and tectonic evolution of the Western U.S. Cordillera, in Burchfiel, B.C., Lipman, P.W., and Zoback, M.L., eds., The Cordilleran Orogen; Conterminous U.S.: Boulder, Colorado, Geological Society of America, The Geol-ogy of North America, v. G-3, p. 57–106.

Miller, M.M., 1987, Dispersed remnants of a northeast Pacific fringing arc: Upper Paleozoic terranes of Permian McCloud faunal affinity, western U.S.: Tectonics, v. 6, p. 807–830, doi: 10.1029/TC006i006p00807.

Morris, E.M., and Wardlaw, B.R., 1986, Conodont ages for limestones of eastern Oregon and their implication for pre-Tertiary mélange terranes, in Vallier, T.L., and Brooks, H.C., eds., Geology of the Blue Mountains Region of Oregon, Idaho, and Washington: Geologic Implications of Paleozoic and Mesozoic Paleontology and Biostratigraphy, Blue Mountains Province, Oregon and Idaho: U.S. Geological Survey Professional Paper 1435, p. 59–63.

Mortimer, N., 1986, Late Triassic, arc-related, potassic ig-neous rocks in the North American Cordillera: Geol-ogy, v. 14, p. 1035–1038, doi: 10.1130/0091-7613 (1986)14<1035:LTAPIR>2.0.CO;2.

Mortimer, N., 1987, The Nicola Group—Late Triassic and Early Jurassic subduction-related volcanism in British Columbia: Canadian Journal of Earth Sciences, v. 24, p. 2521–2536.

Mortimer, N., Van Der Heyden, P., Armstrong, R.L., and Harakal , J., 1990, U-Pb and K-Ar dates related to the timing of magmatism and deformation in the Cache Creek terrane and Quesnellia, southern British Colum-bia: Canadian Journal of Earth Sciences, v. 27, p. 117–123, doi: 10.1139/e90-009.

Nokleberg, W.J., Plafker, G., and Wilson, F.H., 1994, Geol-ogy of south-central Alaska, in Plafker, G., and Berg, H.C., eds., The Geology of Alaska: Boulder, Colorado, Geological Society of America, The Geology of North America, v. G-1, p. 311–366.

Oldow, J.S., 1984, Evolution of a late Mesozoic back-arc fold and thrust belt, northwestern Great Basin, U.S.A.: Tectonophysics, v. 102, p. 245–274, doi: 10.1016/ 0040-1951(84)90016-7.

Oldow, J.S., Bally, A.W., Lallemant, H.G.A., and Leeman, W.P., 1989, Phanerozoic evolution of the North Ameri-can Cordillera: United States and Canada, in Bally, A.W., and Palmer, A.R., eds., The Geology of North America—An overview: Boulder, Colorado, Geologi-cal Society of America, The Geology of North Amer-ica, v. A, p. 139–232.

Paces, J.B., and Miller, J.D., 1993, Precise U-Pb ages of Duluth Complex and related mafic intrusions, north-eastern Minnesota: Geochronological insights into physical, petrogenetic, and paleomagnetic and tectono-magmatic processes associated with the 1.1 Ga mid-continent rift system: Journal of Geophysical Research, v. 98, p. 13,997–14,013, doi: 10.1029/93JB01159.

Parker, K.O., Schwartz, J.J., and Johnson, K., 2008, Petrol-ogy and age of Dixie Butte plutonic rocks, Blue Mountains, NE Oregon [abs.]: Geological Society of America Abstracts with Programs, v. 40, no. 6, p. 154.

Parrish, R.R., and Monger, J.W.H., 1992, New U-Pb dates from southwestern British Columbia, in Radiogenic Age and Isotopic Studies; Report 5: Geological Survey of Canada Paper 91–2, p. 87–108.

Payne, J.D., and Northrup, C.J., 2003, Geologic Map of the Monroe Butte 7.5 Minute Quadrangle, Idaho-Oregon: Idaho Geological Survey Technical Report 03–01, scale 1:24,000.

Pessagno, E.A., Jr., 2006, Faunal evidence for the tectonic transport of Jurassic terranes in Oregon, California, and Mexico, in Snoke, A.W., and Barnes, C.G., eds., Geological Studies in the Klamath Mountains Prov-ince, California and Oregon: A Volume in Honor of William P. Irwin: Geological Society of America Spe-cial Paper 410, p. 31–52, doi: 10.1130/2006.2410(02).

Pessagno, E.A., Jr., and Blome, C.D., 1986, Faunal affini-ties and tectonogenesis of Mesozoic rocks in the Blue Mountains Province of eastern Oregon and western Idaho, in Vallier, T.L., and Brooks, H.C., eds., Geologic

Implications of Paleozoic and Mesozoic Paleontology and Biostratigraphy, Blue Mountains Province, Oregon and Idaho: U.S. Geological Survey Professional Paper 1435, p. 65–78.

Petersen, N.T., Smith, P.L., Mortensen, J.K., Creaser, R.A., and Tipper, H.W., 2004, Provenance of Jurassic sedimentary rocks of south-central Quesnellia, British Columbia: Im-plications for paleogeography: Canadian Journal of Earth Sciences, v. 41, p. 103–125, doi: 10.1139/e03-073.

Phinney, E.J., Mann, P., Coffin, M.F., and Shipley, T., 1999, Sequence stratigraphy and structure of the south-western Ontong Java Plateau adjacent to the North Solomon trench and Solomon Islands: Journal of Geophysical Research, v. 104, p. 20, 449–20,466, doi: 10.1029/1999JB900169.

Pigram, C.J., and Davies, H.L., 1987, Terranes and the ac-cretion history of the New Guinea Orogen: Bureau of Mineral Resources Journal of Australian Geology and Geophysics, v. 10, p. 193–211.

Quinn, M.J., Wright, J.E., and Wyld, S.J., 1997, Happy Creek igneous complex and tectonic evolution of the early Mesozoic arc in the Jackson Mountains, north-west Nevada: Geological Society of America Bul-letin, v. 109, p. 461–482, doi: 10.1130/0016-7606 (1997)109<0461:HCICAT>2.3.CO;2.

Rahl, J.M., Reiners, P.W., Campbell, I.H., Nicolescu, S., and Allen, C.M., 2003, Combined single-grain (U-Th)/He and U/Pb dating of detrital zircons from the Navajo Sand-stone, Utah: Geology, v. 31, p. 761–764, doi: 10.1130/ G19653.1.

Riggs, N.R., Mattinson, J.M., and Busby, C.J., 1993, Corre-lation of Mesozoic eolian strata between the magmatic arc and the Colorado Plateau: New U-Pb geochrono-logic data from southern Arizona: Geological Society of America Bulletin, v. 105, p. 1231–1246, doi: 10.1130/ 0016-7606(1993)105<1231:COJESB>2.3.CO;2.

Riggs, N.R., Lehman, T.M., Gehrels, G.E., and Dickinson, W.R., 1996, Detrital zircon link between headwaters and terminus of the Upper Triassic Chinle-Dockum paleoriver system: Science, v. 273, p. 97–100, doi: 10.1126/science.273.5271.97.

Ross, G.M., and Villeneuve, M., 2003, Provenance of the Mesoproterozoic (1.45 Ga) Belt basin (western North America): Another piece in the pre-Rodinia paleogeo-graphic puzzle: Geological Society of America Bulle-tin, v. 115, p. 1191–1217, doi: 10.1130/B25209.1.

Ross, G.M., Gehrels, G.E., and Patchett, P.J., 1997, Prov-enance of Triassic strata in the Cordilleran miogeo-cline, Western Canada: Bulletin of Canadian Petroleum Geol ogy, v. 45, p. 461–473.

Saccani, E., 1987, Double provenance of sand-size sedi-ments in the southern Aegean forearc basin: Journal of Sedimentary Research, v. 57, p. 736–745, doi: 10.1306/212F8BF2-2B24-11D7-8648000102C1865D.

Saleeby, J.B., 1983, Accretionary tectonics of the North American Cordillera: Annual Review of Earth and Planetary Sciences, v. 11, p. 45–73, doi: 10.1146/ annurev.ea.11.050183.000401.

Saleeby, J.B., 1992, Petrotectonic and paleogeographic set-tings of U.S. Cordilleran ophiolites, in Burchfiel, B.C., Lipman, P.W., and Zoback, M.L., eds., The Cor dilleran Orogen: Conterminous U.S.: Boulder, Colorado, Geo-logical Society of America, The Geology of North America, v. G-3, p. 653–682.

Saleeby, J.B., and Busby-Spera, C., 1992, Early Mesozoic tectonic evolution of the Western U.S. Cordillera, in Burchfiel, B.C., Lipman, P.W., and Zoback, M.L., eds., The Cordilleran Orogen: Conterminous U.S.: Boulder, Colorado, Geological Society of America, The Geol-ogy of North America, v. G-3, p. 107–168.

Saleeby, J., Hannah, J.L., and Varga, R.J., 1987, Iso topic age constraints on middle Paleozoic deformation in the northern Sierra Nevada, California: Geology, v. 15, p. 757–760, doi: 10.1130/0091-7613(1987)15 <757:IACOMP>2.0.CO;2.

San Filippo, R., 2006, The Stratigraphic and Structural Evo-lution of Triassic Rocks North of Huntington, Eastern Oregon [B.S. Honor’s thesis]: Eugene, Oregon, Uni-versity of Oregon, 34 p.

Savage, N.M., and Amundson, C.T., 1979, Middle Devonian (Givetian) conodonts from central Oregon: Journal of Paleontology, v. 53, p. 1395–1400.

Schellart, W.P., Jessell, M.W., and Lister, G.S., 2003, Asymmetric deformation in the backarc region of the Kuril arc, northwest Pacific: New insights from analogue modeling: Tectonics, v. 22, p. 1047, doi: 10.1029/2002TC001473.

Scherer, H.H., 2006, Field, Geochronologic, and Geochemi-cal Constraints on the Early Mesozoic Paleogeographic and Tectonic Evolution of the Central Klamath Moun-tains, California [Ph.D. dissertation]: Palo Alto, Cali-fornia, Stanford University, 199 p.

Scherer, H.H., and Ernst, W.G., 2008, North Fork terrane, Klamath Mountains, California: Geologic, geochemi-cal, and geochronologic evidence for an early Meso-zoic forearc, in Wright, J.E., and Shervais, J.W., eds., Ophiolites, Arcs, and Batholiths: Geological Society of America Special Paper 438, p. 289–309.

Schermer, E.R., Busby, C.J., and Mattinson, J.M., 2002, Paleogeographic and tectonic implications of Juras-sic sedimentary and volcanic sequences in the cen-tral Mojave block, in Glazner, A.F., Walker, J.D., and Bartley, J.M., eds., Geologic Evolution of the Mojave Desert and Southwestern Basin and Range: Geological Society of America Memoir 195, p. 93–115.

Schiarizza, P., Heffernan, S., and Zuber, J., 2002, Geology of Quesnel and Slide Mountain terranes west of Clear-water, south-central British Columbia (92P/9, 10, 15, 16), in Geological Fieldwork 2001: British Columbia Ministry of Energy and Mines Paper 2001–1, p. 1–30.

Schwartz, J.J., Snoke, A.W., Frost, C.D., Barnes, C.G., Gromet, L.P., and Johnson, K., 2010, Analysis of the Wallowa-Baker terrane boundary: Implications for tectonic accretion in the Blue Mountains Province, northeastern Oregon: Geological Society of America Bulletin, v. 122, p. 517–536, doi: 10.1130/B26493.1.

Selverstone, J., Wernicke, B.P., and Aliberti, E.A., 1992, Intra continental subduction and hinged unroofing along the Salmon River suture zone, west central Idaho: Tectonics, v. 11, p. 124–144, doi: 10.1029/91TC02418.

Sharp, W.D., 1988, Pre-Cretaceous crustal evolution in the Sierra Nevada region, California, in Ernst, W.G., ed., Metamorphism and Crustal Evolution, Western Con-terminous United States, Rubey Volume 7: Englewood Cliffs, New Jersey, Prentice-Hall, p. 823–864.

Silberling, N.J., Jones, D.L., Blake, M.C., Jr., and Howell, D.G., 1984, Lithotectonic Terrane Map of the Western Conterminous United States: U.S. Geological Survey Open-File Report 84–0523, p. C1–C43.

Smith, D.L., Wyld, S.J., Wright, J.E., and Miller, E.L., 1993, Progression and timing of Mesozoic crustal shortening in the northern Great Basin, western U.S.A., in Dunne G.C., and McDougall, K., eds., Mesozoic paleogeog-raphy of the Western United States–II: Los Angeles, Pacific Section, Society of Economic Paleontologists and Mineralogists, Book 71, p. 389–406.

Snoke, A.W., 2005, North America: Southern Cordillera, in Selley, R.C., Cocks, L.R.M., and Plimer, I.R., eds., Encyclopedia of Geology, Volume 4: Oxford, UK, Elsevier –Academic Press, p. 61–48.

Snow, C.A., and Ernst, W.G., 2008, Detrital zircon con-straints on sediment distribution and provenance of the Mariposa Formation, central Sierra Nevada foothills, California, in Wright, J.E., and Shervais, J.W., eds., Ophiolites, Arcs, and Batholiths: A Tribute to Cliff Hopson: Geological Society of America Special Paper 438, p. 311–330, doi: 10.1130/2008.2438(11).

Speed, R.C., 1978, Paleogeographic and plate tectonic evo-lution of the early Mesozoic marine province of the western Great Basin, in Howell, D.G., and McDougall, K.A., eds., Mesozoic Paleogeography of the Western United States: Tulsa, Oklahoma, Society of Economic Paleontologists and Mineralogists, Pacific Section, Pa-cific Coast Paleogeography Symposium 2, p. 253–270.

Spurlin, M.S., Gehrels, G.E., and Harwood, D.S., 2000, Detrital zircon geochronology of Upper Paleozoic and Lower Mesozoic strata of the northern Sierra ter-rane, northeastern California, in Soreghan, M.J., and Gehrels , G.E., eds., Paleozoic and Triassic Paleogeog-raphy and Tectonics of Western Nevada and Northern California: Geological Society of America Special Paper 347, p. 89–98.

Surpless, K.D., Graham, S.A., Covault, J.A., and Wooden, J.L., 2006, Does the Great Valley Group contain Jurassic





strata? Reevaluation of the age and early evolution of a classic forearc basin: Geology, v. 34, p. 21–24, doi: 10.1130/G21940.1.

Sylvester, P.J., and Ghaderi, M., 1997, Trace element analy-sis of scheelite by excimer laser ablation–inductively coupled plasma–mass spectrometry (ELA-ICP-MS) using a synthetic silicate glass standard: Chemical Geology, v. 141, p. 49–65, doi: 10.1016/S0009-2541 (97)00057-0.

Tassinari, C.C.G., Bettencourt, J.S., Geraldes, M.C., Macambria , M.J.B., and Lafon, J.M., 2000, The Ama-zonian craton, in Cordani, U.G., Milani, E.J., Filho, A.T., and Campos, D.A., eds., Tectonic Evolution of South America: 31st International Geological Con-gress, Rio de Janeiro, Brazil, Insitut de Recherché pour le Développement, p. 41–99.

Taylor, S.R., and McLennan, S.M., 1985, The Continental Crust: Its Composition and Evolution: Oxford, UK, Blackwell, 312 p.

Thayer, T.P., and Brown, C.E., 1966, Geologic Map of the Aldrich Mountain Quadrangle, Grant County, Oregon: U.S. Geological Survey Geological Quadrangle Map GQ-438, 1:62,500.

Tikoff, B., Kelso, P., Manduca, C., Markley, M.J., and Gillaspy , J., 2001, Lithospheric and crustal reactivation of an ancient plate boundary: The assembly and dis-assembly of the Salmon River suture zone, Idaho, USA, in Holdsworth, R.E., Strachan, R.A., and Magloughlin , J.F., eds., Fault Reactivation: Geological Society of London Special Publication 186, p. 213–231.

Tumpane, K.P., 2010, Age and Isotopic Investigations of the Olds Ferry Terrane and its Relations to Other Terranes of the Blue Mountains Province, Eastern Oregon and West-Central Idaho [M.S. thesis], Boise, Idaho, Boise State University, 201 p.

Tumpane, K.P., and Schmitz, M.D., 2009, New geochrono-logical constraints on the timing of deposition in the Coon Hollow and Weatherby Formations, and corre-lations between the Wallowa and Olds Ferry terranes, Blue Mountains Province, northern U.S. Cordillera: Geological Society of America Abstracts with Pro-grams, v. 41, no. 7, p. 182.

Tumpane, K.P., Crowley, J., Schmitz, M., and Northrup, C.J., 2008, New geochronological constraints on the deposition of the Huntington Formation, Olds Ferry terrane, and implications for the evolution of the Blue Mountains Province: Geological Society of America Abstracts with Programs, v. 40, no. 1, p. 47.

Unruh, D.M., Lund, K., Kuntz, M.A., and Snee, L.W., 2008, Uranium-Lead Zircon Ages and Sr, Nd, and Pb Isotope Geochemistry of Selected Plutonic Rocks from West-ern Idaho: U.S. Geological Survey Open-File Report 2008–1142, 37 p.

Vail, P.R., Mitchum, R.M., and Thompson, S., III, 1977, Seismic stratigraphy and global changes of sea level. Part 3: Relative changes of sea level from coastal on-lap, in Payton, C.E., ed., Seismic Stratigraphy—Ap-plications to Hydrocarbon Exploration: American Association of Petroleum Geologists Memoir 26, p. 63–81.

Vallier, T.L., 1977, The Permian and Triassic Seven Devils Group, Western Idaho and Northeast Oregon: U.S. Geological Survey Bulletin 1437, 58 p.

Vallier, T.L., 1995, Petrology of pre-Tertiary igneous rocks in the Blue Mountains region of Oregon, Idaho, and Washington: Implications for the geologic evolution of a complex island arc, in Vallier, T.L., and Brooks, H.C., eds., Geology of the Blue Mountains Region of Ore-gon, Idaho, and Washington: Petrology and Tectonic Evolution of Pre-Tertiary Rocks of the Blue Mountains Region: U.S. Geological Survey Professional Paper 1438, p. 125–209.

Vallier, T.L., 1998, Islands and Rapids: A Geologic Story of Hells Canyon: Lewiston, Idaho, Confluence Press, Lewis-Clark State College, 151 p.

Van Wagoner, J.C., Mitchum, R.M., Campion, K.M., and Rahmanian, V.D., 1990, Siliciclastic Sequence Stra-tigraphy in Well Logs, Cores, and Outcrops: Concepts for High-Resolution Correlation of Time and Facies: American Association of Petroleum Geologists, Meth-ods in Exploration Series 7, 55 p.

Walker, G.W., and MacLeod, N.S., 1991, Geologic Map of Oregon: U.S. Geological Survey, scale 1:500,000, 2 plates.

Walker, N.W., 1986, U/Pb Geochronologic and Petrologic Studies in the Blue Mountains Terrane, Northeastern Oregon and Westernmost-Central Idaho: Implications for Pre-Tertiary Tectonic Evolution [Ph.D. thesis]: Santa Barbara, California, University of California, Santa Barbara, 224 p.

Walker, N.W., 1989, Early Cretaceous initiation of post-tec-tonic plutonism and the age of the Connor Creek fault, northeastern Oregon: Geological Society of America Abstracts with Programs, v. 21, no. 5, p. 155.

Walker, N.W., 1995, Tectonic implications of U-Pb zircon ages of the Canyon Mountain complex, Sparta com-plex, and related metaplutonic rocks of the Baker ter-rane, northeastern Oregon, in Vallier, T.L., and Brooks, H.C., eds., Geology of the Blue Mountains Region of Oregon, Idaho, and Washington: Petrology and Tectonic Evolution of Pre-Tertiary Rocks of the Blue Mountains Region: U.S. Geological Survey Profes-sional Paper 1438, p. 247–269.

Wernicke, B.P., and Klepacki, D.W., 1988, Escape hypoth-esis for the Stikine block: Geology, v. 16, p. 461–464, doi: 10.1130/0091-7613(1988)016<0461:EHFTSB> 2.3.CO;2.

White, J.D.L., White, D.L., Vallier, T.L., Stanley, G.D., Jr., and Ash, S.R., 1992, Middle Jurassic strata link Wallowa , Olds Ferry, and Izee terranes in the accreted Blue Mountains island arc, northeastern Oregon: Geol ogy, v. 20, p. 729–732, doi: 10.1130/0091-7613 (1992)020<0729:MJSLWO>2.3.CO;2.

Whitmeyer, S.J., and Karlstrom, K.E., 2007, Tectonic model for the Proterozoic growth of North America: Geo-sphere, v. 3, p. 220–259, doi: 10.1130/GES00055.1.

Williams, I.S., 1998, U-Th-Pb geochronology by ion micro-probe, in McKibben, M.A., Shanks, W.C., III, and Ridley, W.I., eds., Applications of Microanalytical Techniques to Understanding Mineralizing Processes: Socorro, New Mexico, Society of Economic Geolo-gists, Reviews in Economic Geology, v. 7, p. 1–35.

Wright, J.E., 1982, Permo-Triassic accretionary subduction complex, southwestern Klamath Mountains, northern California: Journal of Geophysical Research, v. 87, p. 3805–3818, doi: 10.1029/JB087iB05p03805.

Wright, J.E., and Fahan, M.R., 1988, An expanded view of Jurassic orogenesis in the western United States Cordillera: Middle Jurassic (pre-Nevadan) regional metamorphism and thrust faulting within an active arc environment, Klamath Mountains, California: Geologi-cal Society of America Bulletin, v. 100, p. 859–876, doi: 10.1130/0016-7606(1988)100<0859:AEVOJO> 2.3.CO;2.

Wright, J.E., and Wyld, S.J., 2006, Gondwanan, Iapetan, Cordilleran interactions: A geodynamic model for the Paleozoic tectonic evolution of the North American Cordillera, in Haggart, J.E., Enkin, R.J., and Monger, J.W.H., eds., Paleogeography of the North American Cordillera: Evidence For and Against Large-Scale Dis-placements: Geological Association of Canada Special Paper 46, p. 377–408.

Wright, J.E., and Wyld, S.J., 2007, Alternative tectonic model for Late Jurassic through Early Cretaceous evo-

lution of the Great Valley Group, California, in Cloos, M., Carlson, W.D., Gilbert, M.C., Liou, J.G., and Soren-sen, S.S., eds., Convergent Margin Terranes and Asso-ciated Regions: A Tribute to W.G. Ernst: Geological Society of America Special Paper 419, p. 81–95.

Wyld, S.J., 1990, Paleozoic and Mesozoic rocks of the Pine Forest Range, northwest Nevada, and their relation to volcanic arc assemblages of the western U.S. Cor-dillera, in Harwood, D.S., and Miller, M.M., eds., Late Paleozoic and Early Mesozoic Paleogeographic Rela-tions: Klamath Mountains, Sierra Nevada, and Related Rocks: Geological Society of America Special Paper 255, p. 219–237.

Wyld, S.J., 1996, Early Jurassic deformation in the Pine Forest Range, northwest Nevada, and implications for Cordilleran tectonics: Tectonics, v. 15, p. 566–583, doi: 10.1029/95TC03693.

Wyld, S.J., 2000, Triassic evolution of the arc and back-arc of northwest Nevada, and evidence for extensional tectonism, in Soreghan, M.J., and Gehrels, G.E., eds., Paleozoic and Triassic Paleogeography and Tectonics of western Nevada and Northern California: Geologi-cal Society of America Special Paper 347, p. 185–207.

Wyld, S.J., 2002, Structural evolution of a Mesozoic back-arc fold-and-thrust belt in the U.S. Cordillera: New evidence from northern Nevada: Geological Society of America Bulletin, v. 114, p. 1452–1468, doi: 10.1130/ 0016-7606(2002)114<1452:SEOAMB>2.0.CO;2.

Wyld, S.J., and Wright, J.E., 2001, New evidence for Creta-ceous strike-slip faulting in the United States Cordillera and implications for terrane-displacement, deforma-tion patterns, and plutonism: American Journal of Sci-ence, v. 301, p. 150–181, doi: 10.2475/ajs.301.2.150.

Wyld, S.J., and Wright, J.E., 2005, Early Cretaceous, margin-parallel, dextral faulting and terrane transla-tion in the U.S. Cordillera [abs.]: Geological Society of America Abstracts with Programs, v. 37, no. 4, p. 102.

Wyld, S.J., Quinn, M.J., and Wright, J.E., 1996, Anoma-lous(?) Early Jurassic deformation in the western United States Cordillera: Geology, v. 24, p. 1037–1040, doi: 10.1130/0091-7613(1996)024<1037:AEJDIT> 2.3.CO;2.

Wyld, S.J., Rogers, J.W., and Copeland, P., 2003, Metamor-phic evolution of the Luning-Fencemaker fold-thrust belt, Nevada: Illite crystallinity, metamorphic petrol-ogy, and 40Ar/39Ar geochronology: The Journal of Geol ogy, v. 111, p. 17–38, doi: 10.1086/344663.

Wyld, S.J., Umhoefer, P.J., and Wright, J.E., 2006, Recon-structing northern Cordilleran terranes along known Cretaceous and Cenozoic strike-slip faults: Impli-cations for the Baja British Columbia hypothesis and other models, in Haggart, J.W., Enkin, R.J., and Monger , J.W.H., eds., Paleogeography of the North American Cordillera: Evidence For and Against Large-Scale Displacements: Geological Association of Can-ada Special Paper 46, p. 277–298.

Yancey, T.E., and Stanley, G.D., Jr., 1999, Giant alato-form bivalves in the Upper Triassic of western North America: Palaeontology, v. 42, no. 1, p. 1–23, doi: 10.1111/1475-4983.00060.

Yeh, K.Y., 1989, Studies of Radiolaria from Fields Creek Formation, east-central Oregon, U.S.A.: National Museum of Natural Science, Taiwan, Bulletin 1, p. 43–109.

Science editor: nancy riggS aSSociate editor: Quentin crowley

ManuScript received 29 January 2010 reviSed ManuScript received 29 SepteMber 2010 ManuScript accepted 29 october 2010

Printed in the USA



Documents

Early Mesozoic paleogeography and tectonic evolution of